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btf_encoder: Generate BTF_KIND_TAG from llvm annotations 

The following is an example with latest upstream clang:

  $ cat t.c
  #define __tag1 __attribute__((btf_tag("tag1")))
  #define __tag2 __attribute__((btf_tag("tag2")))

  struct t {
          int a:1 __tag1;
          int b __tag2;
  } __tag1 __tag2;

  int g __tag1 __attribute__((section(".data..percpu")));

  int __tag1 foo(struct t *a1, int a2 __tag2) {
    return a1->b + a2 + g;
  }

  $ clang -O2 -g -c t.c
  $ pahole -JV t.o
  Found per-CPU symbol 'g' at address 0x0
  Found 1 per-CPU variables!
  Found 1 functions!
  File t.o:
  [1] INT int size=4 nr_bits=32 encoding=SIGNED
  [2] PTR (anon) type_id=3
  [3] STRUCT t size=8
        a type_id=1 bitfield_size=1 bits_offset=0
        b type_id=1 bitfield_size=0 bits_offset=32
  [4] TAG tag1 type_id=3 component_idx=0
  [5] TAG tag2 type_id=3 component_idx=1
  [6] TAG tag1 type_id=3 component_idx=-1
  [7] TAG tag2 type_id=3 component_idx=-1
  [8] FUNC_PROTO (anon) return=1 args=(2 a1, 1 a2)
  [9] FUNC foo type_id=8
  [10] TAG tag2 type_id=9 component_idx=1
  [11] TAG tag1 type_id=9 component_idx=-1
  search cu 't.c' for percpu global variables.
  Variable 'g' from CU 't.c' at address 0x0 encoded
  [12] VAR g type=1 linkage=1
  [13] TAG tag1 type_id=12 component_idx=-1
  [14] DATASEC .data..percpu size=4 vlen=1
        type=12 offset=0 size=4
  $ ...

With additional option --skip_encoding_btf_tag, pahole doesn't
generate BTF_KIND_TAGs any more.

  $ pahole -JV --skip_encoding_btf_tag t.o
  Found per-CPU symbol 'g' at address 0x0
  Found 1 per-CPU variables!
  Found 1 functions!
  File t.o:
  [1] INT int size=4 nr_bits=32 encoding=SIGNED
  [2] PTR (anon) type_id=3
  [3] STRUCT t size=8
        a type_id=1 bitfield_size=1 bits_offset=0
        b type_id=1 bitfield_size=0 bits_offset=32
  [4] FUNC_PROTO (anon) return=1 args=(2 a1, 1 a2)
  [5] FUNC foo type_id=4
  search cu 't.c' for percpu global variables.
  Variable 'g' from CU 't.c' at address 0x0 encoded
  [6] VAR g type=1 linkage=1
  [7] DATASEC .data..percpu size=4 vlen=1
        type=6 offset=0 size=4
  $ ...

Signed-off-by: Yonghong Song <yhs@fb.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: bpf@vger.kernel.org
Cc: dwarves@vger.kernel.org
Cc: kernel-team@fb.com
Link: https://lore.kernel.org/r/20210922021332.2287418-1-yhs@fb.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Yonghong Song 2021-09-21 19:13:32 -07:00 committed by Arnaldo Carvalho de Melo
parent aa8c494e65
commit e38e89e853
1 changed files with 62 additions and 1 deletions
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63
btf_encoder.c
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@ -141,6 +141,7 @@ static const char * const btf_kind_str[NR_BTF_KINDS] = {
[BTF_KIND_VAR] = "VAR",
[BTF_KIND_DATASEC] = "DATASEC",
[BTF_KIND_FLOAT] = "FLOAT",
[BTF_KIND_TAG] = "TAG",
};
static const char *btf__printable_name(const struct btf *btf, uint32_t offset)
@ -644,6 +645,26 @@ static int32_t btf_encoder__add_datasec(struct btf_encoder *encoder, const char
return id;
}
static int32_t btf_encoder__add_tag(struct btf_encoder *encoder, const char *value, uint32_t type,
int component_idx)
{
struct btf *btf = encoder->btf;
const struct btf_type *t;
int32_t id;
id = btf__add_tag(btf, value, type, component_idx);
if (id > 0) {
t = btf__type_by_id(btf, id);
btf_encoder__log_type(encoder, t, false, true, "type_id=%u component_idx=%d",
t->type, component_idx);
} else {
btf__log_err(btf, BTF_KIND_TAG, value, true, "component_idx=%d Error emitting BTF type",
component_idx);
}
return id;
}
/*
* This corresponds to the same macro defined in
* include/linux/kallsyms.h
@ -1158,6 +1179,7 @@ static int btf_encoder__encode_cu_variables(struct btf_encoder *encoder, struct
struct variable *var = tag__variable(pos);
uint32_t size, type, linkage;
const char *name, *dwarf_name;
struct llvm_annotation *annot;
const struct tag *tag;
uint64_t addr;
int id;
@ -1244,6 +1266,15 @@ static int btf_encoder__encode_cu_variables(struct btf_encoder *encoder, struct
goto out;
}
list_for_each_entry(annot, &var->annots, node) {
int tag_type_id = btf_encoder__add_tag(encoder, annot->value, id, annot->component_idx);
if (tag_type_id < 0) {
fprintf(stderr, "error: failed to encode tag '%s' to variable '%s' with component_idx %d\n",
annot->value, name, annot->component_idx);
goto out;
}
}
/*
* add a BTF_VAR_SECINFO in encoder->percpu_secinfo, which will be added into
* encoder->types later when we add BTF_VAR_DATASEC.
@ -1359,6 +1390,8 @@ void btf_encoder__delete(struct btf_encoder *encoder)
int btf_encoder__encode_cu(struct btf_encoder *encoder, struct cu *cu)
{
uint32_t type_id_off = btf__get_nr_types(encoder->btf);
struct llvm_annotation *annot;
int btf_type_id, tag_type_id;
uint32_t core_id;
struct function *fn;
struct tag *pos;
@ -1378,7 +1411,7 @@ int btf_encoder__encode_cu(struct btf_encoder *encoder, struct cu *cu)
}
cu__for_each_type(cu, core_id, pos) {
int32_t btf_type_id = btf_encoder__encode_tag(encoder, pos, type_id_off);
btf_type_id = btf_encoder__encode_tag(encoder, pos, type_id_off);
if (btf_type_id < 0 ||
tag__check_id_drift(pos, core_id, btf_type_id, type_id_off)) {
@ -1396,6 +1429,25 @@ int btf_encoder__encode_cu(struct btf_encoder *encoder, struct cu *cu)
encoder->has_index_type = true;
}
cu__for_each_type(cu, core_id, pos) {
struct namespace *ns;
if (pos->tag != DW_TAG_structure_type && pos->tag != DW_TAG_union_type)
continue;
btf_type_id = type_id_off + core_id;
ns = tag__namespace(pos);
list_for_each_entry(annot, &ns->annots, node) {
tag_type_id = btf_encoder__add_tag(encoder, annot->value, btf_type_id, annot->component_idx);
if (tag_type_id < 0) {
fprintf(stderr, "error: failed to encode tag '%s' to %s '%s' with component_idx %d\n",
annot->value, pos->tag == DW_TAG_structure_type ? "struct" : "union",
namespace__name(ns), annot->component_idx);
goto out;
}
}
}
cu__for_each_function(cu, core_id, fn) {
int btf_fnproto_id, btf_fn_id;
const char *name;
@ -1436,6 +1488,15 @@ int btf_encoder__encode_cu(struct btf_encoder *encoder, struct cu *cu)
printf("error: failed to encode function '%s'\n", function__name(fn));
goto out;
}
list_for_each_entry(annot, &fn->annots, node) {
tag_type_id = btf_encoder__add_tag(encoder, annot->value, btf_fn_id, annot->component_idx);
if (tag_type_id < 0) {
fprintf(stderr, "error: failed to encode tag '%s' to func %s with component_idx %d\n",
annot->value, name, annot->component_idx);
goto out;
}
}
}
if (!encoder->skip_encoding_vars)