38b123494b
On x86-64, the procedure linkage table (PLT) is used to 1. Call external function. 2. Call internal IFUNC function. The best implementation is selected for the target processor at run-time. 3. Act as the canonical function address. 4. Support LD_AUDIT to audit external function calls. 5. Support LD_PROFILE to profile external function calls. PLT looks like: PLT0: push GOT[1] jmp *GOT[2] nop PLT1: jmp *GOT[name1_index] push name1_reloc_index jmp PLT0 GOT is an array of addresses. Initially the GOT entry of name1 is filled with the address of the "push name1_reloc_index" instruction. The function, name1, is called via "jmp *GOT[name1]" in the PLT entry. Even when lazy binding is disabled by "-z now", the PLT0 entry may still be used with LD_AUDIT or LD_PROFILE if PLT entry is used for canonical function address. When linker is invoked with "-z bndplt", a different PLT layout in .plt is used: PLT0: push GOT[1] bnd jmp *GOT[2] nop PLT1: push name1_reloc_index bnd jmp PLT0 nop together with a second PLT section, .pl.bnd: PLT1: bnd jmp *GOT[name1_index] nop where the GOT entry of name1 is filled with the address of the push instruction of the corresponding entry in .plt. 1. With lazy binding, when the external function, name1, is called the first time, dynamic linker is called via PLT0 to update GOT[name1_index] with the actual address of name1 and transfers control to name1 afterwards. 2. PLT is also used to call a local IFUNC function, name1, run-time loader updates GOT[name1_index] when loading the module. This patch 1. Remove PLT layout configurations from x86-64 backend_data. 2. Add generic, lay and non-lazy PLT layout configurations to x86-64 link_hash_table. Generic PLT layout includes the PLT entry templates, information how to update the first instruction in PLT and PLT eh_frame informaton, which are initialized in x86-64 setup_gnu_properties, based on "-z bndplt" and target selection. PLT section alignment is also set to PLT entry size for non-NaCl target. 3. Remove elf_x86_64_create_dynamic_sections. create_dynamic_sections isn't always called, but GOT relocations need GOT relocations. Instead, create all x86-64 specific dynamic sections with alignment to their entry size in x86-64 setup_gnu_properties, which initializes elf.dynobj, so that x86-64 check_relocs can be simplified. 4. Rewrite elf_x86_64_get_synthetic_symtab to check PLT sections against all dynamic relocations to support both lazy and non-lazy PLTs. There is no change in PLT. The only externally visible change is the improvement of synthetic PLT symbols for .plt.got. bfd/ * elf64-x86-64.c (PLT_ENTRY_SIZE): Renamed to ... (LAZY_PLT_ENTRY_SIZE): This. (NON_LAZY_PLT_ENTRY_SIZE): New. (elf_x86_64_plt0_entry): Renamed to ... (elf_x86_64_lazy_plt0_entry): This. (elf_x86_64_plt_entry): Renamed to ... (elf_x86_64_lazy_plt_entry): This. (elf_x86_64_bnd_plt0_entry): Renamed to ... (elf_x86_64_lazy_bnd_plt0_entry): This. (elf_x86_64_legacy_plt_entry): Removed. (elf_x86_64_bnd_plt_entry): Renamed to ... (elf_x86_64_lazy_bnd_plt_entry): This. (elf_x86_64_legacy_plt2_entry): Renamed to ... (elf_x86_64_non_lazy_plt_entry): This. (elf_x86_64_bnd_plt2_entry): Renamed to ... (elf_x86_64_non_lazy_bnd_plt_entry): This. (elf_x86_64_eh_frame_plt): Renamed to ... (elf_x86_64_eh_frame_lazy_plt): This. (elf_x86_64_eh_frame_bnd_plt): Renamed to ... (elf_x86_64_eh_frame_lazy_bnd_plt): This. (elf_x86_64_eh_frame_plt_got): Renamed to ... (elf_x86_64_eh_frame_non_lazy_plt): This. (elf_x86_64_lazy_plt_layout): New. (elf_x86_64_non_lazy_plt_layout): Likewise. (elf_x86_64_plt_layout): Likewise. (elf_x86_64_backend_data): Remove PLT layout information. Add os for target system. (GET_PLT_ENTRY_SIZE): Removed. (elf_x86_64_lazy_plt): New. (elf_x86_64_non_lazy_plt): Likewise. (elf_x86_64_lazy_bnd_plt): Likewise. (elf_x86_64_non_lazy_bnd_plt): Likewise. (elf_x86-64_arch_bed): Updated. (elf_x86_64_link_hash_table): Add plt, lazy_plt and non_lazy_plt. (elf_x86_64_create_dynamic_sections): Removed. (elf_x86_64_check_relocs): Don't check elf.dynobj. Don't call _bfd_elf_create_ifunc_sections nor _bfd_elf_create_got_section. (elf_x86-64_adjust_dynamic_symbol): Updated. (elf_x86_64_allocate_dynrelocs): Updated. Pass 0 as PLT header size to _bfd_elf_allocate_ifunc_dyn_relocs and don't allocate size for PLT0 if there is no PLT0. Get plt_entry_size from non_lazy_plt for non-lazy PLT entries. (elf_x86_64_size_dynamic_sections): Updated. Get plt_entry_size from non_lazy_plt for non-lazy PLT entries. (elf_x86-64_relocate_section): Updated. Properly get PLT index if there is no PLT0. (elf_x86_64_finish_dynamic_symbol): Updated. Fill the first slot in the PLT entry with generic PLT layout. Fill the non-lazy PLT entries with non-lazy PLT layout. Don't fill the second and third slots in the PLT entry if there is no PLT0. (elf_x86_64_finish_dynamic_sections): Updated. Don't fill PLT0 if there is no PLT0. Set sh_entsize on the .plt.got section. (compare_relocs): New. (elf_x86_64_plt_type): Likewise. (elf_x86_64_plt): Likewise. (elf_x86_64_nacl_plt): New. Forward declaration. (elf_x86_64_get_plt_sym_val): Removed. (elf_x86_64_get_synthetic_symtab): Rewrite to check PLT sections against all dynamic relocations. (elf_x86_64_link_setup_gnu_properties): New function. (elf_backend_create_dynamic_sections): Updated. (elf_backend_setup_gnu_properties): New. (elf_x86_64_nacl_plt): New. (elf_x86_64_nacl_arch_bed): Updated. ld/ * testsuite/ld-ifunc/ifunc-16-x86-64-now.d: New file. * testsuite/ld-ifunc/ifunc-2-local-x86-64-now.d: Likewise. * testsuite/ld-ifunc/ifunc-2-x86-64-now.d: Likewise. * testsuite/ld-ifunc/pr17154-x86-64-now.d: Likewise. * testsuite/ld-x86-64/bnd-branch-1-now.d: Likewise. * testsuite/ld-x86-64/bnd-ifunc-1-now.d: Likewise. * testsuite/ld-x86-64/bnd-ifunc-2-now.d: Likewise. * testsuite/ld-x86-64/bnd-plt-1-now.d: Likewise. * testsuite/ld-x86-64/mpx3n.dd: Likewise. * testsuite/ld-x86-64/mpx4n.dd: Likewise. * testsuite/ld-x86-64/plt-main-bnd-now.rd: Likewise. * testsuite/ld-x86-64/plt2.dd: Likewise. * testsuite/ld-x86-64/plt2.rd: Likewise. * testsuite/ld-x86-64/plt2.s: Likewise. * testsuite/ld-x86-64/pr20830a-now.d: Likewise. * testsuite/ld-x86-64/pr20830b-now.d: Likewise. * testsuite/ld-x86-64/pr21038a-now.d: Likewise. * testsuite/ld-x86-64/pr21038b-now.d: Likewise. * testsuite/ld-x86-64/pr21038c-now.d: Likewise. * testsuite/ld-x86-64/load1b-nacl.d: Updated. * testsuite/ld-x86-64/load1b.d: Likewise. * testsuite/ld-x86-64/plt-main-bnd.dd: Likewise. * testsuite/ld-x86-64/pr20253-1h.d: Likewise. * testsuite/ld-x86-64/pr20830a.d: Update the .plt.got section with func@plt. * testsuite/ld-x86-64/pr20830b.d: Likewise. * testsuite/ld-x86-64/pr21038a.d: Likewise. * testsuite/ld-x86-64/pr21038c.d: Likewise. * testsuite/ld-x86-64/mpx.exp: Add some -z now tests. * testsuite/ld-x86-64/x86-64.exp: Likewise. |
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.. | ||
emulparams | ||
emultempl | ||
po | ||
scripttempl | ||
testsuite | ||
.gitignore | ||
aclocal.m4 | ||
ChangeLog | ||
ChangeLog-0001 | ||
ChangeLog-0203 | ||
ChangeLog-2004 | ||
ChangeLog-2005 | ||
ChangeLog-2006 | ||
ChangeLog-2007 | ||
ChangeLog-2008 | ||
ChangeLog-2009 | ||
ChangeLog-2010 | ||
ChangeLog-2011 | ||
ChangeLog-2012 | ||
ChangeLog-2013 | ||
ChangeLog-2014 | ||
ChangeLog-2015 | ||
ChangeLog-2016 | ||
ChangeLog-9197 | ||
ChangeLog-9899 | ||
config.in | ||
configure | ||
configure.ac | ||
configure.host | ||
configure.tgt | ||
deffile.h | ||
deffilep.y | ||
dep-in.sed | ||
elf-hints-local.h | ||
fdl.texi | ||
gen-doc.texi | ||
genscrba.sh | ||
genscripts.sh | ||
h8-doc.texi | ||
ld.h | ||
ld.texinfo | ||
ldbuildid.c | ||
ldbuildid.h | ||
ldcref.c | ||
ldctor.c | ||
ldctor.h | ||
ldemul.c | ||
ldemul.h | ||
ldexp.c | ||
ldexp.h | ||
ldfile.c | ||
ldfile.h | ||
ldgram.y | ||
ldint.texinfo | ||
ldlang.c | ||
ldlang.h | ||
ldlex-wrapper.c | ||
ldlex.h | ||
ldlex.l | ||
ldmain.c | ||
ldmain.h | ||
ldmisc.c | ||
ldmisc.h | ||
ldver.c | ||
ldver.h | ||
ldwrite.c | ||
ldwrite.h | ||
lexsup.c | ||
MAINTAINERS | ||
Makefile.am | ||
Makefile.in | ||
mri.c | ||
mri.h | ||
NEWS | ||
pe-dll.c | ||
pe-dll.h | ||
pep-dll.c | ||
pep-dll.h | ||
plugin.c | ||
plugin.h | ||
README | ||
stamp-h.in | ||
sysdep.h | ||
testplug2.c | ||
testplug3.c | ||
testplug4.c | ||
testplug.c | ||
TODO |
README for LD
This is the GNU linker. It is distributed with other "binary
utilities" which should be in ../binutils. See ../binutils/README for
more general notes, including where to send bug reports.
There are many features of the linker:
* The linker uses a Binary File Descriptor library (../bfd)
that it uses to read and write object files. This helps
insulate the linker itself from the format of object files.
* The linker supports a number of different object file
formats. It can even handle multiple formats at once:
Read two input formats and write a third.
* The linker can be configured for cross-linking.
* The linker supports a control language.
* There is a user manual (ld.texinfo), as well as the
beginnings of an internals manual (ldint.texinfo).
Installation
============
See ../binutils/README.
If you want to make a cross-linker, you may want to specify
a different search path of -lfoo libraries than the default.
You can do this by setting the LIB_PATH variable in ./Makefile
or using the --with-lib-path configure switch.
To build just the linker, make the target all-ld from the top level
directory (one directory above this one).
Porting to a new target
=======================
See the ldint.texinfo manual.
Reporting bugs etc
===========================
See ../binutils/README.
Known problems
==============
The Solaris linker normally exports all dynamic symbols from an
executable. The GNU linker does not do this by default. This is
because the GNU linker tries to present the same interface for all
similar targets (in this case, all native ELF targets). This does not
matter for normal programs, but it can make a difference for programs
which try to dlopen an executable, such as PERL or Tcl. You can make
the GNU linker export all dynamic symbols with the -E or
--export-dynamic command line option.
HP/UX 9.01 has a shell bug that causes the linker scripts to be
generated incorrectly. The symptom of this appears to be "fatal error
- scanner input buffer overflow" error messages. There are various
workarounds to this:
* Build and install bash, and build with "make SHELL=bash".
* Update to a version of HP/UX with a working shell (e.g., 9.05).
* Replace "(. ${srcdir}/scripttempl/${SCRIPT_NAME}.sc)" in
genscripts.sh with "sh ${srcdir}..." (no parens) and make sure the
emulparams script used exports any shell variables it sets.
Copyright (C) 2012-2017 Free Software Foundation, Inc.
Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.