btf_encoder: Support btf_type_tag attribute
[$ ~] cat t.c
#define __tag1 __attribute__((btf_type_tag("tag1")))
#define __tag2 __attribute__((btf_type_tag("tag2")))
int __tag1 * __tag1 __tag2 *g __attribute__((section(".data..percpu")));
[$ ~] clang -O2 -g -c t.c
[$ ~] pahole -JV t.o
Found per-CPU symbol 'g' at address 0x0
Found 1 per-CPU variables!
File t.o:
[1] TYPE_TAG tag1 type_id=5
[2] TYPE_TAG tag2 type_id=1
[3] PTR (anon) type_id=2
[4] TYPE_TAG tag1 type_id=6
[5] PTR (anon) type_id=4
[6] INT int size=4 nr_bits=32 encoding=SIGNED
search cu 't.c' for percpu global variables.
Variable 'g' from CU 't.c' at address 0x0 encoded
[7] VAR g type=3 linkage=1
[8] DATASEC .data..percpu size=8 vlen=1
type=7 offset=0 size=8
[$ ~]
You can see for the source:
int __tag1 * __tag1 __tag2 *g __attribute__((section(".data..percpu")));
the following type chain is generated:
var -> ptr -> tag2 -> tag1 -> ptr -> tag1 -> int
The following shows pahole option "--skip_encoding_btf_type_tag" can be
used to prevent BTF_KIND_TYPE_TAG generation.
[$ ~] pahole -JV t.o --skip_encoding_btf_type_tag
Found per-CPU symbol 'g' at address 0x0
Found 1 per-CPU variables!
File t.o:
[1] PTR (anon) type_id=2
[2] PTR (anon) type_id=3
[3] INT int size=4 nr_bits=32 encoding=SIGNED
search cu 't.c' for percpu global variables.
Variable 'g' from CU 't.c' at address 0x0 encoded
[4] VAR g type=1 linkage=1
[5] DATASEC .data..percpu size=8 vlen=1
type=4 offset=0 size=8
[$ ~]
Committer testing:
$ rm -f t.o; clang -O2 -g -c t.c
$ llvm-dwarfdump t.o
t.o: file format elf64-x86-64
.debug_info contents:
0x00000000: Compile Unit: length = 0x0000005e, format = DWARF32, version = 0x0004, abbr_offset = 0x0000, addr_size = 0x08 (next unit at 0x00000062)
0x0000000b: DW_TAG_compile_unit
DW_AT_producer ("clang version 14.0.0 (https://github.com/llvm/llvm-project 0d3add216f04b99ed1db1a05c39975d4a9c83e6b)")
DW_AT_language (DW_LANG_C99)
DW_AT_name ("t.c")
DW_AT_stmt_list (0x00000000)
DW_AT_comp_dir ("/var/home/acme/git/pahole")
0x0000001e: DW_TAG_variable
DW_AT_name ("g")
DW_AT_type (0x00000033 "int **")
DW_AT_external (true)
DW_AT_decl_file ("/var/home/acme/git/pahole/t.c")
DW_AT_decl_line (3)
DW_AT_location (DW_OP_addr 0x0)
0x00000033: DW_TAG_pointer_type
DW_AT_type (0x0000004b "int *")
0x00000038: DW_TAG_LLVM_annotation
DW_AT_name ("btf_type_tag")
DW_AT_const_value ("tag1")
0x00000041: DW_TAG_LLVM_annotation
DW_AT_name ("btf_type_tag")
DW_AT_const_value ("tag2")
0x0000004a: NULL
0x0000004b: DW_TAG_pointer_type
DW_AT_type (0x0000005a "int")
0x00000050: DW_TAG_LLVM_annotation
DW_AT_name ("btf_type_tag")
DW_AT_const_value ("tag1")
0x00000059: NULL
0x0000005a: DW_TAG_base_type
DW_AT_name ("int")
DW_AT_encoding (DW_ATE_signed)
DW_AT_byte_size (0x04)
0x00000061: NULL
$ pahole -JV t.o
Found per-CPU symbol 'g' at address 0x0
Found 1 per-CPU variables!
File t.o:
[1] TYPE_TAG tag1 type_id=5
[2] TYPE_TAG tag2 type_id=1
[3] PTR (anon) type_id=2
[4] TYPE_TAG tag1 type_id=6
[5] PTR (anon) type_id=4
[6] INT int size=4 nr_bits=32 encoding=SIGNED
search cu 't.c' for percpu global variables.
Variable 'g' from CU 't.c' at address 0x0 encoded
[7] VAR g type=3 linkage=1
[8] DATASEC .data..percpu size=8 vlen=1
type=7 offset=0 size=8
⬢[acme@toolbox pahole]$ pahole -JV t.o --skip_encoding_btf_type_tag
Found per-CPU symbol 'g' at address 0x0
Found 1 per-CPU variables!
File t.o:
[1] PTR (anon) type_id=2
[2] PTR (anon) type_id=3
[3] INT int size=4 nr_bits=32 encoding=SIGNED
search cu 't.c' for percpu global variables.
Variable 'g' from CU 't.c' at address 0x0 encoded
[4] VAR g type=1 linkage=1
[5] DATASEC .data..percpu size=8 vlen=1
type=4 offset=0 size=8
$
Signed-off-by: Yonghong Song <yhs@fb.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: bpf@vger.kernel.org
Cc: dwarves@vger.kernel.org
Cc: kernel-team@fb.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Yonghong Song
Arnaldo Carvalho de Melo
parent
3da248c328
commit
d99d551930
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@ -143,6 +143,7 @@ static const char * const btf_kind_str[NR_BTF_KINDS] = {
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[BTF_KIND_DATASEC] = "DATASEC",
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[BTF_KIND_FLOAT] = "FLOAT",
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[BTF_KIND_DECL_TAG] = "DECL_TAG",
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[BTF_KIND_TYPE_TAG] = "TYPE_TAG",
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};
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static const char *btf__printable_name(const struct btf *btf, uint32_t offset)
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@ -393,6 +394,9 @@ static int32_t btf_encoder__add_ref_type(struct btf_encoder *encoder, uint16_t k
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case BTF_KIND_TYPEDEF:
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id = btf__add_typedef(btf, name, type);
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break;
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case BTF_KIND_TYPE_TAG:
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id = btf__add_type_tag(btf, name, type);
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break;
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case BTF_KIND_FWD:
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id = btf__add_fwd(btf, name, kind_flag);
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break;
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@ -862,6 +866,9 @@ static int btf_encoder__encode_tag(struct btf_encoder *encoder, struct tag *tag,
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case DW_TAG_typedef:
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name = namespace__name(tag__namespace(tag));
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return btf_encoder__add_ref_type(encoder, BTF_KIND_TYPEDEF, ref_type_id, name, false);
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case DW_TAG_LLVM_annotation:
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name = tag__btf_type_tag(tag)->value;
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return btf_encoder__add_ref_type(encoder, BTF_KIND_TYPE_TAG, ref_type_id, name, false);
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case DW_TAG_structure_type:
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case DW_TAG_union_type:
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case DW_TAG_class_type:
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@ -637,6 +637,11 @@ static inline struct btf_type_tag_ptr_type *tag__btf_type_tag_ptr(struct tag *ta
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return (struct btf_type_tag_ptr_type *)tag;
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}
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static inline struct btf_type_tag_type *tag__btf_type_tag(struct tag *tag)
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{
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return (struct btf_type_tag_type *)tag;
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}
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/** struct namespace - base class for enums, structs, unions, typedefs, etc
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*
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* @tags - class_member, enumerators, etc
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