Re: [PATCH dwarves 2/2] btf_encoder: generate BTF_KIND_DECL_TAGs for typedef btf_decl_tag attributes

[Yonghong Song <yhs@fb.com>]

On 11/1/21 7:58 PM, Andrii Nakryiko wrote:
> On Wed, Oct 27, 2021 at 4:08 PM Yonghong Song <yhs@fb.com> wrote:
>>
>> Emit BTF BTF_KIND_DECL_TAGs for btf_decl_tag attributes attached to
>> typedef declarations. The following is a simple example:
>>    $ cat t.c
>>      #define __tag1 __attribute__((btf_decl_tag("tag1")))
>>      #define __tag2 __attribute__((btf_decl_tag("tag2")))
>>      typedef struct { int a; int b; } __t __tag1 __tag2;
>>      __t g;
>>    $ clang -O2 -g -c t.c
>>    $ pahole -JV t.o
>>      btf_encoder__new: 't.o' doesn't have '.data..percpu' section
>>      Found 0 per-CPU variables!
>>      File t.o:
>>      [1] TYPEDEF __t type_id=2
>>      [2] STRUCT (anon) size=8
>>              a type_id=3 bits_offset=0
>>              b type_id=3 bits_offset=32
>>      [3] INT int size=4 nr_bits=32 encoding=SIGNED
>>      [4] DECL_TAG tag1 type_id=1 component_idx=-1
>>      [5] DECL_TAG tag2 type_id=1 component_idx=-1
>>
>> Signed-off-by: Yonghong Song <yhs@fb.com>
>> ---
>>   btf_encoder.c | 12 +++++++++---
>>   1 file changed, 9 insertions(+), 3 deletions(-)
>>
>> diff --git a/btf_encoder.c b/btf_encoder.c
>> index 40f6aa3..2f1f4ae 100644
>> --- a/btf_encoder.c
>> +++ b/btf_encoder.c
>> @@ -1437,19 +1437,25 @@ int btf_encoder__encode_cu(struct btf_encoder *encoder, struct cu *cu)
>>          }
>>
>>          cu__for_each_type(cu, core_id, pos) {
>> +               const char *tag_name = "typedef";
>>                  struct namespace *ns;
>>
>> -               if (pos->tag != DW_TAG_structure_type && pos->tag != DW_TAG_union_type)
>> +               if (pos->tag != DW_TAG_structure_type && pos->tag != DW_TAG_union_type &&
>> +                   pos->tag != DW_TAG_typedef)
>>                          continue;
>>
>> +               if (pos->tag == DW_TAG_structure_type)
>> +                       tag_name = "struct";
>> +               else if (pos->tag == DW_TAG_union_type)
>> +                       tag_name = "union";
> 
> nit: switch instead of these two related sets of if/else blocks would be cleaner

Sure. Will make the change in v2.

> 
> 
>> +
>>                  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_decl_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);
>> +                                       annot->value, tag_name, namespace__name(ns), annot->component_idx);
>>                                  goto out;
>>                          }
>>                  }
>> --
>> 2.30.2
>>