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

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On 11/1/21 7:58 PM, Andrii Nakryiko wrote:
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

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




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