linux/scripts/recordmcount.pl

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ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
#!/usr/bin/perl -w
# (c) 2008, Steven Rostedt <srostedt@redhat.com>
# Licensed under the terms of the GNU GPL License version 2
#
# recordmcount.pl - makes a section called __mcount_loc that holds
# all the offsets to the calls to mcount.
#
#
# What we want to end up with this is that each object file will have a
# section called __mcount_loc that will hold the list of pointers to mcount
# callers. After final linking, the vmlinux will have within .init.data the
# list of all callers to mcount between __start_mcount_loc and __stop_mcount_loc.
# Later on boot up, the kernel will read this list, save the locations and turn
# them into nops. When tracing or profiling is later enabled, these locations
# will then be converted back to pointers to some function.
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
#
# This is no easy feat. This script is called just after the original
# object is compiled and before it is linked.
#
# When parse this object file using 'objdump', the references to the call
# sites are offsets from the section that the call site is in. Hence, all
# functions in a section that has a call site to mcount, will have the
# offset from the beginning of the section and not the beginning of the
# function.
#
# But where this section will reside finally in vmlinx is undetermined at
# this point. So we can't use this kind of offsets to record the final
# address of this call site.
#
# The trick is to change the call offset referring the start of a section to
# referring a function symbol in this section. During the link step, 'ld' will
# compute the final address according to the information we record.
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
#
# e.g.
#
# .section ".sched.text", "ax"
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
# [...]
# func1:
# [...]
# call mcount (offset: 0x10)
# [...]
# ret
# .globl fun2
# func2: (offset: 0x20)
# [...]
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
# [...]
# ret
# func3:
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
# [...]
# call mcount (offset: 0x30)
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
# [...]
#
# Both relocation offsets for the mcounts in the above example will be
# offset from .sched.text. If we choose global symbol func2 as a reference and
# make another file called tmp.s with the new offsets:
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
#
# .section __mcount_loc
# .quad func2 - 0x10
# .quad func2 + 0x10
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
#
# We can then compile this tmp.s into tmp.o, and link it back to the original
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
# object.
#
# In our algorithm, we will choose the first global function we meet in this
# section as the reference. But this gets hard if there is no global functions
# in this section. In such a case we have to select a local one. E.g. func1:
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
#
# .section ".sched.text", "ax"
# func1:
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
# [...]
# call mcount (offset: 0x10)
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
# [...]
# ret
# func2:
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
# [...]
# call mcount (offset: 0x20)
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
# [...]
# .section "other.section"
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
#
# If we make the tmp.s the same as above, when we link together with
# the original object, we will end up with two symbols for func1:
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
# one local, one global. After final compile, we will end up with
# an undefined reference to func1 or a wrong reference to another global
# func1 in other files.
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
#
# Since local objects can reference local variables, we need to find
# a way to make tmp.o reference the local objects of the original object
# file after it is linked together. To do this, we convert func1
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
# into a global symbol before linking tmp.o. Then after we link tmp.o
# we will only have a single symbol for func1 that is global.
# We can convert func1 back into a local symbol and we are done.
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
#
# Here are the steps we take:
#
# 1) Record all the local and weak symbols by using 'nm'
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
# 2) Use objdump to find all the call site offsets and sections for
# mcount.
# 3) Compile the list into its own object.
# 4) Do we have to deal with local functions? If not, go to step 8.
# 5) Make an object that converts these local functions to global symbols
# with objcopy.
# 6) Link together this new object with the list object.
# 7) Convert the local functions back to local symbols and rename
# the result as the original object.
# 8) Link the object with the list object.
# 9) Move the result back to the original object.
#
use strict;
my $P = $0;
$P =~ s@.*/@@g;
my $V = '0.1';
if ($#ARGV != 11) {
print "usage: $P arch endian bits objdump objcopy cc ld nm rm mv is_module inputfile\n";
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
print "version: $V\n";
exit(1);
}
my ($arch, $endian, $bits, $objdump, $objcopy, $cc,
$ld, $nm, $rm, $mv, $is_module, $inputfile) = @ARGV;
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
# This file refers to mcount and shouldn't be ftraced, so lets' ignore it
if ($inputfile =~ m,kernel/trace/ftrace\.o$,) {
exit(0);
}
# Acceptable sections to record.
my %text_sections = (
".text" => 1,
".ref.text" => 1,
".sched.text" => 1,
".spinlock.text" => 1,
".irqentry.text" => 1,
".kprobes.text" => 1,
".text.unlikely" => 1,
);
# Note: we are nice to C-programmers here, thus we skip the '||='-idiom.
$objdump = 'objdump' if (!$objdump);
$objcopy = 'objcopy' if (!$objcopy);
$cc = 'gcc' if (!$cc);
$ld = 'ld' if (!$ld);
$nm = 'nm' if (!$nm);
$rm = 'rm' if (!$rm);
$mv = 'mv' if (!$mv);
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
#print STDERR "running: $P '$arch' '$objdump' '$objcopy' '$cc' '$ld' " .
# "'$nm' '$rm' '$mv' '$inputfile'\n";
my %locals; # List of local (static) functions
my %weak; # List of weak functions
my %convert; # List of local functions used that needs conversion
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
my $type;
my $local_regex; # Match a local function (return function)
my $weak_regex; # Match a weak function (return function)
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
my $section_regex; # Find the start of a section
my $function_regex; # Find the name of a function
# (return offset and func name)
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
my $mcount_regex; # Find the call site to mcount (return offset)
my $mcount_adjust; # Address adjustment to mcount offset
my $alignment; # The .align value to use for $mcount_section
my $section_type; # Section header plus possible alignment command
my $can_use_local = 0; # If we can use local function references
# Shut up recordmcount if user has older objcopy
my $quiet_recordmcount = ".tmp_quiet_recordmcount";
my $print_warning = 1;
$print_warning = 0 if ( -f $quiet_recordmcount);
##
# check_objcopy - whether objcopy supports --globalize-symbols
#
# --globalize-symbols came out in 2.17, we must test the version
# of objcopy, and if it is less than 2.17, then we can not
# record local functions.
sub check_objcopy
{
open (IN, "$objcopy --version |") or die "error running $objcopy";
while (<IN>) {
if (/objcopy.*\s(\d+)\.(\d+)/) {
$can_use_local = 1 if ($1 > 2 || ($1 == 2 && $2 >= 17));
last;
}
}
close (IN);
if (!$can_use_local && $print_warning) {
print STDERR "WARNING: could not find objcopy version or version " .
"is less than 2.17.\n" .
"\tLocal function references are disabled.\n";
open (QUIET, ">$quiet_recordmcount");
printf QUIET "Disables the warning from recordmcount.pl\n";
close QUIET;
}
}
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
if ($arch =~ /(x86(_64)?)|(i386)/) {
if ($bits == 64) {
$arch = "x86_64";
} else {
$arch = "i386";
}
}
#
# We base the defaults off of i386, the other archs may
# feel free to change them in the below if statements.
#
$local_regex = "^[0-9a-fA-F]+\\s+t\\s+(\\S+)";
$weak_regex = "^[0-9a-fA-F]+\\s+([wW])\\s+(\\S+)";
$section_regex = "Disassembly of section\\s+(\\S+):";
$function_regex = "^([0-9a-fA-F]+)\\s+<(.*?)>:";
$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s(mcount|__fentry__)\$";
$section_type = '@progbits';
$mcount_adjust = 0;
$type = ".long";
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
if ($arch eq "x86_64") {
$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s(mcount|__fentry__)([+-]0x[0-9a-zA-Z]+)?\$";
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
$type = ".quad";
$alignment = 8;
$mcount_adjust = -1;
# force flags for this arch
$ld .= " -m elf_x86_64";
$objdump .= " -M x86-64";
$objcopy .= " -O elf64-x86-64";
$cc .= " -m64";
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
} elsif ($arch eq "i386") {
$alignment = 4;
$mcount_adjust = -1;
# force flags for this arch
$ld .= " -m elf_i386";
$objdump .= " -M i386";
$objcopy .= " -O elf32-i386";
$cc .= " -m32";
} elsif ($arch eq "s390" && $bits == 32) {
$mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_390_32\\s+_mcount\$";
$mcount_adjust = -4;
$alignment = 4;
$ld .= " -m elf_s390";
$cc .= " -m31";
} elsif ($arch eq "s390" && $bits == 64) {
$mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_390_(PC|PLT)32DBL\\s+_mcount\\+0x2\$";
$mcount_adjust = -8;
$alignment = 8;
$type = ".quad";
$ld .= " -m elf64_s390";
$cc .= " -m64";
} elsif ($arch eq "sh") {
$alignment = 2;
# force flags for this arch
$ld .= " -m shlelf_linux";
$objcopy .= " -O elf32-sh-linux";
$cc .= " -m32";
} elsif ($arch eq "powerpc") {
$local_regex = "^[0-9a-fA-F]+\\s+t\\s+(\\.?\\S+)";
$function_regex = "^([0-9a-fA-F]+)\\s+<(\\.?.*?)>:";
$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s\\.?_mcount\$";
if ($bits == 64) {
$type = ".quad";
}
} elsif ($arch eq "arm") {
$alignment = 2;
$section_type = '%progbits';
$mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_ARM_(CALL|PC24|THM_CALL)" .
"\\s+(__gnu_mcount_nc|mcount)\$";
} elsif ($arch eq "ia64") {
$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
$type = "data8";
if ($is_module eq "0") {
$cc .= " -mconstant-gp";
}
} elsif ($arch eq "sparc64") {
# In the objdump output there are giblets like:
# 0000000000000000 <igmp_net_exit-0x18>:
# As there's some data blobs that get emitted into the
# text section before the first instructions and the first
# real symbols. We don't want to match that, so to combat
# this we use '\w' so we'll match just plain symbol names,
# and not those that also include hex offsets inside of the
# '<>' brackets. Actually the generic function_regex setting
# could safely use this too.
$function_regex = "^([0-9a-fA-F]+)\\s+<(\\w*?)>:";
# Sparc64 calls '_mcount' instead of plain 'mcount'.
$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
$alignment = 8;
$type = ".xword";
$ld .= " -m elf64_sparc";
$cc .= " -m64";
$objcopy .= " -O elf64-sparc";
MIPS: Tracing: Add dynamic function tracer support With dynamic function tracer, by default, _mcount is defined as an "empty" function, it returns directly without any more action . When enabling it in user-space, it will jump to a real tracing function(ftrace_caller), and do the real job for us. Differ from the static function tracer, dynamic function tracer provides two functions ftrace_make_call()/ftrace_make_nop() to enable/disable the tracing of some indicated kernel functions(set_ftrace_filter). In the -v4 version, the implementation of this support is basically the same as X86 version does: _mcount is implemented as an empty function and ftrace_caller is implemented as a real tracing function respectively. But in this version, to support module tracing with the help of -mlong-calls in arch/mips/Makefile: MODFLAGS += -mlong-calls. The stuff becomes a little more complex. We need to cope with two different type of calling to _mcount. For the kernel part, the calling to _mcount(result of "objdump -hdr vmlinux"). is like this: 108: 03e0082d move at,ra 10c: 0c000000 jal 0 <fpcsr_pending> 10c: R_MIPS_26 _mcount 10c: R_MIPS_NONE *ABS* 10c: R_MIPS_NONE *ABS* 110: 00020021 nop For the module with -mlong-calls, it looks like this: c: 3c030000 lui v1,0x0 c: R_MIPS_HI16 _mcount c: R_MIPS_NONE *ABS* c: R_MIPS_NONE *ABS* 10: 64630000 daddiu v1,v1,0 10: R_MIPS_LO16 _mcount 10: R_MIPS_NONE *ABS* 10: R_MIPS_NONE *ABS* 14: 03e0082d move at,ra 18: 0060f809 jalr v1 In the kernel version, there is only one "_mcount" string for every kernel function, so, we just need to match this one in mcount_regex of scripts/recordmcount.pl, but in the module version, we need to choose one of the two to match. Herein, I choose the first one with "R_MIPS_HI16 _mcount". and In the kernel verion, without module tracing support, we just need to replace "jal _mcount" by "jal ftrace_caller" to do real tracing, and filter the tracing of some kernel functions via replacing it by a nop instruction. but as we have described before, the instruction "jal ftrace_caller" only left 32bit length for the address of ftrace_caller, it will fail when calling from the module space. so, herein, we must replace something else. the basic idea is loading the address of ftrace_caller to v1 via changing these two instructions: lui v1,0x0 addiu v1,v1,0 If we want to enable the tracing, we need to replace the above instructions to: lui v1, HI_16BIT_ftrace_caller addiu v1, v1, LOW_16BIT_ftrace_caller If we want to stop the tracing of the indicated kernel functions, we just need to replace the "jalr v1" to a nop instruction. but we need to replace two instructions and encode the above two instructions oursevles. Is there a simpler solution? Yes! Here it is, in this version, we put _mcount and ftrace_caller together, which means the address of _mcount and ftrace_caller is the same: _mcount: ftrace_caller: j ftrace_stub nop ...(do real tracing here)... ftrace_stub: jr ra move ra, at By default, the kernel functions call _mcount, and then jump to ftrace_stub and return. and when we want to do real tracing, we just need to remove that "j ftrace_stub", and it will run through the two "nop" instructions and then do the real tracing job. what about filtering job? we just need to do this: lui v1, hi_16bit_of_mcount <--> b 1f (0x10000004) addiu v1, v1, low_16bit_of_mcount move at, ra jalr v1 nop 1f: (rec->ip + 12) In linux-mips64, there will be some local symbols, whose name are prefixed by $L, which need to be filtered. thanks goes to Steven for writing the mips64-specific function_regex. In a conclusion, with RISC, things becomes easier with such a "stupid" trick, RISC is something like K.I.S.S, and also, there are lots of "simple" tricks in the whole ftrace support, thanks goes to Steven and the other folks for providing such a wonderful tracing framework! Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com> Cc: Nicholas Mc Guire <der.herr@hofr.at> Cc: zhangfx@lemote.com Cc: Wu Zhangjin <wuzhangjin@gmail.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: linux-kernel@vger.kernel.org Cc: linux-mips@linux-mips.org Patchwork: http://patchwork.linux-mips.org/patch/675/ Acked-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2009-11-20 13:34:32 +01:00
} elsif ($arch eq "mips") {
# To enable module support, we need to enable the -mlong-calls option
# of gcc for module, after using this option, we can not get the real
# offset of the calling to _mcount, but the offset of the lui
# instruction or the addiu one. herein, we record the address of the
# first one, and then we can replace this instruction by a branch
# instruction to jump over the profiling function to filter the
# indicated functions, or swith back to the lui instruction to trace
# them, which means dynamic tracing.
#
# c: 3c030000 lui v1,0x0
# c: R_MIPS_HI16 _mcount
# c: R_MIPS_NONE *ABS*
# c: R_MIPS_NONE *ABS*
# 10: 64630000 daddiu v1,v1,0
# 10: R_MIPS_LO16 _mcount
# 10: R_MIPS_NONE *ABS*
# 10: R_MIPS_NONE *ABS*
# 14: 03e0082d move at,ra
# 18: 0060f809 jalr v1
#
# for the kernel:
#
# 10: 03e0082d move at,ra
# 14: 0c000000 jal 0 <loongson_halt>
# 14: R_MIPS_26 _mcount
# 14: R_MIPS_NONE *ABS*
# 14: R_MIPS_NONE *ABS*
# 18: 00020021 nop
if ($is_module eq "0") {
$mcount_regex = "^\\s*([0-9a-fA-F]+): R_MIPS_26\\s+_mcount\$";
MIPS: Tracing: Add dynamic function tracer support With dynamic function tracer, by default, _mcount is defined as an "empty" function, it returns directly without any more action . When enabling it in user-space, it will jump to a real tracing function(ftrace_caller), and do the real job for us. Differ from the static function tracer, dynamic function tracer provides two functions ftrace_make_call()/ftrace_make_nop() to enable/disable the tracing of some indicated kernel functions(set_ftrace_filter). In the -v4 version, the implementation of this support is basically the same as X86 version does: _mcount is implemented as an empty function and ftrace_caller is implemented as a real tracing function respectively. But in this version, to support module tracing with the help of -mlong-calls in arch/mips/Makefile: MODFLAGS += -mlong-calls. The stuff becomes a little more complex. We need to cope with two different type of calling to _mcount. For the kernel part, the calling to _mcount(result of "objdump -hdr vmlinux"). is like this: 108: 03e0082d move at,ra 10c: 0c000000 jal 0 <fpcsr_pending> 10c: R_MIPS_26 _mcount 10c: R_MIPS_NONE *ABS* 10c: R_MIPS_NONE *ABS* 110: 00020021 nop For the module with -mlong-calls, it looks like this: c: 3c030000 lui v1,0x0 c: R_MIPS_HI16 _mcount c: R_MIPS_NONE *ABS* c: R_MIPS_NONE *ABS* 10: 64630000 daddiu v1,v1,0 10: R_MIPS_LO16 _mcount 10: R_MIPS_NONE *ABS* 10: R_MIPS_NONE *ABS* 14: 03e0082d move at,ra 18: 0060f809 jalr v1 In the kernel version, there is only one "_mcount" string for every kernel function, so, we just need to match this one in mcount_regex of scripts/recordmcount.pl, but in the module version, we need to choose one of the two to match. Herein, I choose the first one with "R_MIPS_HI16 _mcount". and In the kernel verion, without module tracing support, we just need to replace "jal _mcount" by "jal ftrace_caller" to do real tracing, and filter the tracing of some kernel functions via replacing it by a nop instruction. but as we have described before, the instruction "jal ftrace_caller" only left 32bit length for the address of ftrace_caller, it will fail when calling from the module space. so, herein, we must replace something else. the basic idea is loading the address of ftrace_caller to v1 via changing these two instructions: lui v1,0x0 addiu v1,v1,0 If we want to enable the tracing, we need to replace the above instructions to: lui v1, HI_16BIT_ftrace_caller addiu v1, v1, LOW_16BIT_ftrace_caller If we want to stop the tracing of the indicated kernel functions, we just need to replace the "jalr v1" to a nop instruction. but we need to replace two instructions and encode the above two instructions oursevles. Is there a simpler solution? Yes! Here it is, in this version, we put _mcount and ftrace_caller together, which means the address of _mcount and ftrace_caller is the same: _mcount: ftrace_caller: j ftrace_stub nop ...(do real tracing here)... ftrace_stub: jr ra move ra, at By default, the kernel functions call _mcount, and then jump to ftrace_stub and return. and when we want to do real tracing, we just need to remove that "j ftrace_stub", and it will run through the two "nop" instructions and then do the real tracing job. what about filtering job? we just need to do this: lui v1, hi_16bit_of_mcount <--> b 1f (0x10000004) addiu v1, v1, low_16bit_of_mcount move at, ra jalr v1 nop 1f: (rec->ip + 12) In linux-mips64, there will be some local symbols, whose name are prefixed by $L, which need to be filtered. thanks goes to Steven for writing the mips64-specific function_regex. In a conclusion, with RISC, things becomes easier with such a "stupid" trick, RISC is something like K.I.S.S, and also, there are lots of "simple" tricks in the whole ftrace support, thanks goes to Steven and the other folks for providing such a wonderful tracing framework! Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com> Cc: Nicholas Mc Guire <der.herr@hofr.at> Cc: zhangfx@lemote.com Cc: Wu Zhangjin <wuzhangjin@gmail.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: linux-kernel@vger.kernel.org Cc: linux-mips@linux-mips.org Patchwork: http://patchwork.linux-mips.org/patch/675/ Acked-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2009-11-20 13:34:32 +01:00
} else {
$mcount_regex = "^\\s*([0-9a-fA-F]+): R_MIPS_HI16\\s+_mcount\$";
}
$objdump .= " -Melf-trad".$endian."mips ";
if ($endian eq "big") {
$endian = " -EB ";
$ld .= " -melf".$bits."btsmip";
} else {
$endian = " -EL ";
$ld .= " -melf".$bits."ltsmip";
}
$cc .= " -mno-abicalls -fno-pic -mabi=" . $bits . $endian;
$ld .= $endian;
if ($bits == 64) {
$function_regex =
"^([0-9a-fA-F]+)\\s+<(.|[^\$]L.*?|\$[^L].*?|[^\$][^L].*?)>:";
$type = ".dword";
}
} elsif ($arch eq "microblaze") {
# Microblaze calls '_mcount' instead of plain 'mcount'.
$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
} elsif ($arch eq "blackfin") {
$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s__mcount\$";
$mcount_adjust = -4;
} elsif ($arch eq "tilegx" || $arch eq "tile") {
# Default to the newer TILE-Gx architecture if only "tile" is given.
$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s__mcount\$";
$type = ".quad";
$alignment = 8;
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
} else {
die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD";
}
my $text_found = 0;
my $read_function = 0;
my $opened = 0;
my $mcount_section = "__mcount_loc";
my $dirname;
my $filename;
my $prefix;
my $ext;
if ($inputfile =~ m,^(.*)/([^/]*)$,) {
$dirname = $1;
$filename = $2;
} else {
$dirname = ".";
$filename = $inputfile;
}
if ($filename =~ m,^(.*)(\.\S),) {
$prefix = $1;
$ext = $2;
} else {
$prefix = $filename;
$ext = "";
}
my $mcount_s = $dirname . "/.tmp_mc_" . $prefix . ".s";
my $mcount_o = $dirname . "/.tmp_mc_" . $prefix . ".o";
check_objcopy();
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
#
# Step 1: find all the local (static functions) and weak symbols.
# 't' is local, 'w/W' is weak
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
#
open (IN, "$nm $inputfile|") || die "error running $nm";
while (<IN>) {
if (/$local_regex/) {
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
$locals{$1} = 1;
} elsif (/$weak_regex/) {
$weak{$2} = $1;
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
}
}
close(IN);
my @offsets; # Array of offsets of mcount callers
my $ref_func; # reference function to use for offsets
my $offset = 0; # offset of ref_func to section beginning
##
# update_funcs - print out the current mcount callers
#
# Go through the list of offsets to callers and write them to
# the output file in a format that can be read by an assembler.
#
sub update_funcs
{
return unless ($ref_func and @offsets);
# Sanity check on weak function. A weak function may be overwritten by
# another function of the same name, making all these offsets incorrect.
if (defined $weak{$ref_func}) {
die "$inputfile: ERROR: referencing weak function" .
" $ref_func for mcount\n";
}
# is this function static? If so, note this fact.
if (defined $locals{$ref_func}) {
# only use locals if objcopy supports globalize-symbols
if (!$can_use_local) {
return;
}
$convert{$ref_func} = 1;
}
# Loop through all the mcount caller offsets and print a reference
# to the caller based from the ref_func.
if (!$opened) {
open(FILE, ">$mcount_s") || die "can't create $mcount_s\n";
$opened = 1;
print FILE "\t.section $mcount_section,\"a\",$section_type\n";
print FILE "\t.align $alignment\n" if (defined($alignment));
}
foreach my $cur_offset (@offsets) {
printf FILE "\t%s %s + %d\n", $type, $ref_func, $cur_offset - $offset;
}
}
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
#
# Step 2: find the sections and mcount call sites
#
ftrace: test for running of recordmcount.pl twice on an object Impact: fix failure of dynamic function tracer selftest In a course of development, a developer does several makes on their kernel. Sometimes, the make might do something abnormal. In the case of running the recordmcount.pl script on an object twice, the script will duplicate all the calls to mcount in the __mcount_loc section. On boot up, the dynamic function tracer is careful when it modifies code, and performs several consistency checks. One is to not modify the call site if it is not what it expects it to be. If a function call site is listed twice, the first entry will convert the site to a nop, and the second will fail because it expected to see a call to mcount, but instead it sees a nop. Thus, the function tracer is disabled. Eric Sesterhenn reported seeing: [ 1.055440] ftrace: converting mcount calls to 0f 1f 44 00 00 [ 1.055568] ftrace: allocating 29418 entries in 116 pages [ 1.061000] ------------[ cut here ]------------ [ 1.061000] WARNING: at kernel/trace/ftrace.c:441 [...] [ 1.060000] ---[ end trace 4eaa2a86a8e2da23 ]--- [ 1.060000] ftrace failed to modify [<c0118072>] check_corruption+0x3/0x2d [ 1.060000] actual: 0f:1f:44:00:00 This warning shows that check_corruption+0x3 already had a nop in its place (0x0f1f440000). After compiling another kernel the problem went away. Later Eric Paris notice the same type of issue. Luckily, he saved the vmlinux file that caused it. In the file we found a bunch of duplicate mcount call site records, which lead us to the script. Perhaps this problem only happens to people named Eric. This patch changes the script to test if the __mcount_loc already exists in the object file, and if it does, it will print out an error message and kill the compile. Reported-by: Eric Sesterhenn <snakebyte@gmx.de> Reported-by: Eric Paris <eparis@redhat.com> Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-01-17 05:18:31 +01:00
open(IN, "$objdump -hdr $inputfile|") || die "error running $objdump";
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
my $text;
# read headers first
ftrace: test for running of recordmcount.pl twice on an object Impact: fix failure of dynamic function tracer selftest In a course of development, a developer does several makes on their kernel. Sometimes, the make might do something abnormal. In the case of running the recordmcount.pl script on an object twice, the script will duplicate all the calls to mcount in the __mcount_loc section. On boot up, the dynamic function tracer is careful when it modifies code, and performs several consistency checks. One is to not modify the call site if it is not what it expects it to be. If a function call site is listed twice, the first entry will convert the site to a nop, and the second will fail because it expected to see a call to mcount, but instead it sees a nop. Thus, the function tracer is disabled. Eric Sesterhenn reported seeing: [ 1.055440] ftrace: converting mcount calls to 0f 1f 44 00 00 [ 1.055568] ftrace: allocating 29418 entries in 116 pages [ 1.061000] ------------[ cut here ]------------ [ 1.061000] WARNING: at kernel/trace/ftrace.c:441 [...] [ 1.060000] ---[ end trace 4eaa2a86a8e2da23 ]--- [ 1.060000] ftrace failed to modify [<c0118072>] check_corruption+0x3/0x2d [ 1.060000] actual: 0f:1f:44:00:00 This warning shows that check_corruption+0x3 already had a nop in its place (0x0f1f440000). After compiling another kernel the problem went away. Later Eric Paris notice the same type of issue. Luckily, he saved the vmlinux file that caused it. In the file we found a bunch of duplicate mcount call site records, which lead us to the script. Perhaps this problem only happens to people named Eric. This patch changes the script to test if the __mcount_loc already exists in the object file, and if it does, it will print out an error message and kill the compile. Reported-by: Eric Sesterhenn <snakebyte@gmx.de> Reported-by: Eric Paris <eparis@redhat.com> Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-01-17 05:18:31 +01:00
my $read_headers = 1;
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
while (<IN>) {
if ($read_headers && /$mcount_section/) {
#
# Somehow the make process can execute this script on an
# object twice. If it does, we would duplicate the mcount
# section and it will cause the function tracer self test
# to fail. Check if the mcount section exists, and if it does,
# warn and exit.
#
print STDERR "ERROR: $mcount_section already in $inputfile\n" .
"\tThis may be an indication that your build is corrupted.\n" .
"\tDelete $inputfile and try again. If the same object file\n" .
"\tstill causes an issue, then disable CONFIG_DYNAMIC_FTRACE.\n";
exit(-1);
}
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
# is it a section?
if (/$section_regex/) {
ftrace: test for running of recordmcount.pl twice on an object Impact: fix failure of dynamic function tracer selftest In a course of development, a developer does several makes on their kernel. Sometimes, the make might do something abnormal. In the case of running the recordmcount.pl script on an object twice, the script will duplicate all the calls to mcount in the __mcount_loc section. On boot up, the dynamic function tracer is careful when it modifies code, and performs several consistency checks. One is to not modify the call site if it is not what it expects it to be. If a function call site is listed twice, the first entry will convert the site to a nop, and the second will fail because it expected to see a call to mcount, but instead it sees a nop. Thus, the function tracer is disabled. Eric Sesterhenn reported seeing: [ 1.055440] ftrace: converting mcount calls to 0f 1f 44 00 00 [ 1.055568] ftrace: allocating 29418 entries in 116 pages [ 1.061000] ------------[ cut here ]------------ [ 1.061000] WARNING: at kernel/trace/ftrace.c:441 [...] [ 1.060000] ---[ end trace 4eaa2a86a8e2da23 ]--- [ 1.060000] ftrace failed to modify [<c0118072>] check_corruption+0x3/0x2d [ 1.060000] actual: 0f:1f:44:00:00 This warning shows that check_corruption+0x3 already had a nop in its place (0x0f1f440000). After compiling another kernel the problem went away. Later Eric Paris notice the same type of issue. Luckily, he saved the vmlinux file that caused it. In the file we found a bunch of duplicate mcount call site records, which lead us to the script. Perhaps this problem only happens to people named Eric. This patch changes the script to test if the __mcount_loc already exists in the object file, and if it does, it will print out an error message and kill the compile. Reported-by: Eric Sesterhenn <snakebyte@gmx.de> Reported-by: Eric Paris <eparis@redhat.com> Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-01-17 05:18:31 +01:00
$read_headers = 0;
# Only record text sections that we know are safe
$read_function = defined($text_sections{$1});
# print out any recorded offsets
update_funcs();
# reset all markers and arrays
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
$text_found = 0;
undef($ref_func);
undef(@offsets);
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
# section found, now is this a start of a function?
} elsif ($read_function && /$function_regex/) {
$text_found = 1;
$text = $2;
# if this is either a local function or a weak function
# keep looking for functions that are global that
# we can use safely.
if (!defined($locals{$text}) && !defined($weak{$text})) {
$ref_func = $text;
$read_function = 0;
$offset = hex $1;
} else {
# if we already have a function, and this is weak, skip it
tracing: do not use functions starting with .L in recordmcount.pl On Wed, 5 Aug 2009, Ingo Molnar wrote: > * Dave Airlie <airlied@gmail.com> wrote: > > > Hey, > > > > So I spent 3-4 hrs today (I'm stupid yes) tracking down a .o > > breakage by blaming rawhide gcc/binutils as I was using make > > V=1and seeing only the compiler chain running, > > Hm, is this that powerpc related build bug you just reported? Well we tracked it down and it is powerpc64 specific. Seems that in drivers/hwmon/lm93.c there's a function called: LM93_IN_FROM_REG() But PPC64 has function descriptors and the real function names (the ones you see in objdump) start with a '.'. Thus this in objdump you have: Disassembly of section .text: 0000000000000000 <.LM93_IN_FROM_REG>: 0: 7c 08 02 a6 mflr r0 4: fb 81 ff e0 std r28,-32(r1) The function name used is .LM93_IN_FROM_REG. But gcc considers symbols that start with ".L" as a special symbol that is used inside the assembly stage. The nm passed into recordmcount uses the --synthetic option which shows the ".L" symbols (my runs outside of the build did not include the --synthetic option, so my older patch worked). We see the function as a local. Now to capture all the locations that use "mcount" we need to have a reference to link into the object file a list of mcount callers. We need a reference that will not disappear. We try to use a global function and if that does not work, we use a local function as a reference. But to relink the section back into the object, we need to make it global. In this case, we run objcopy using --globalize-symbol and --localize-symbol to convert the symbol into a global symbol, link the mcount list, then convert it back to a local symbol. This works great except for this case. .L* symbols can not be converted into a global symbol, and the mcount section referencing it will remain unresolved. Reported-by: Dave Airlie <airlied@gmail.com> LKML-Reference: <alpine.DEB.2.00.0908052011590.5010@gandalf.stny.rr.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2009-08-06 04:00:14 +02:00
if (!defined($ref_func) && !defined($weak{$text}) &&
# PPC64 can have symbols that start with .L and
# gcc considers these special. Don't use them!
$text !~ /^\.L/) {
$ref_func = $text;
$offset = hex $1;
}
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
}
}
# is this a call site to mcount? If so, record it to print later
if ($text_found && /$mcount_regex/) {
push(@offsets, (hex $1) + $mcount_adjust);
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
}
}
# dump out anymore offsets that may have been found
update_funcs();
ftrace: create __mcount_loc section This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-14 21:45:07 +02:00
# If we did not find any mcount callers, we are done (do nothing).
if (!$opened) {
exit(0);
}
close(FILE);
#
# Step 3: Compile the file that holds the list of call sites to mcount.
#
`$cc -o $mcount_o -c $mcount_s`;
my @converts = keys %convert;
#
# Step 4: Do we have sections that started with local functions?
#
if ($#converts >= 0) {
my $globallist = "";
my $locallist = "";
foreach my $con (@converts) {
$globallist .= " --globalize-symbol $con";
$locallist .= " --localize-symbol $con";
}
my $globalobj = $dirname . "/.tmp_gl_" . $filename;
my $globalmix = $dirname . "/.tmp_mx_" . $filename;
#
# Step 5: set up each local function as a global
#
`$objcopy $globallist $inputfile $globalobj`;
#
# Step 6: Link the global version to our list.
#
`$ld -r $globalobj $mcount_o -o $globalmix`;
#
# Step 7: Convert the local functions back into local symbols
#
`$objcopy $locallist $globalmix $inputfile`;
# Remove the temp files
`$rm $globalobj $globalmix`;
} else {
my $mix = $dirname . "/.tmp_mx_" . $filename;
#
# Step 8: Link the object with our list of call sites object.
#
`$ld -r $inputfile $mcount_o -o $mix`;
#
# Step 9: Move the result back to the original object.
#
`$mv $mix $inputfile`;
}
# Clean up the temp files
`$rm $mcount_o $mcount_s`;
exit(0);