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

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On Wed, Oct 27, 2021 at 4:08 PM Yonghong Song <yhs@xxxxxx> 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@xxxxxx>
> ---
>  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


> +
>                 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
>



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