On Sun, Sep 19, 2021 at 5:36 PM Yonghong Song <yhs@xxxxxx> wrote:
>
> 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@xxxxxx>
> ---
> btf_encoder.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 45 insertions(+)
>
[...]
> @@ -1244,6 +1266,10 @@ static int btf_encoder__encode_cu_variables(struct btf_encoder *encoder, struct
> goto out;
> }
>
> + list_for_each_entry(annot, &var->annots, node) {
> + btf_encoder__add_tag(encoder, annot->value, id, annot->component_idx);
check errors?
> + }
> +
> /*
> * 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 +1385,7 @@ 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;
> uint32_t core_id;
> struct function *fn;
> struct tag *pos;
> @@ -1396,6 +1423,20 @@ 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;
> + int btf_type_id;
> +
> + 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) {
> + btf_encoder__add_tag(encoder, annot->value, btf_type_id, annot->component_idx);
same, this can fail
> + }
> + }
> +
> cu__for_each_function(cu, core_id, fn) {
> int btf_fnproto_id, btf_fn_id;
> const char *name;
> @@ -1436,6 +1477,10 @@ 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) {
> + btf_encoder__add_tag(encoder, annot->value, btf_fn_id, annot->component_idx);
and here as well
> + }
> }
>
> if (!encoder->skip_encoding_vars)
> --
> 2.30.2
>
