On 1/7/19 11:38 PM, Andrii Nakryiko wrote:
> When dealing with BTF encoding of multiple CUs, special `void` type
> should be handled explicitly. This is already handled for all BTF
> types except recently added FUNC_PROTO. Without this fix, any `void`
> type directly referenced from FUNC_PROTO will turn into last type
> from previous CU (see example below, for FUNC_PROTO [4]).
>
> $ cat test1.c
> void (*foo)(void);
>
> int main() {
> return 0;
> }
>
> $ cat test2.c
> void (*bar)(void);
>
> $ cc -g test1.c test2.c -o test
>
> Without fix:
>
> $ LLVM_OBJCOPY=objcopy ~/local/pahole/build/pahole -JV /tmp/test
> File /tmp/test:
> [1] INT int size=4 bit_offset=0 nr_bits=32 encoding=SIGNED
> [2] FUNC_PROTO (anon) return=0 args=(void)
> [3] PTR (anon) type_id=2
> [4] FUNC_PROTO (anon) return=3 args=(void)
> [5] PTR (anon) type_id=4
>
> With fix:
>
> $ LLVM_OBJCOPY=objcopy ~/local/pahole/build/pahole -JV /tmp/test
> File /tmp/test:
> [1] INT int size=4 bit_offset=0 nr_bits=32 encoding=SIGNED
> [2] FUNC_PROTO (anon) return=0 args=(void)
> [3] PTR (anon) type_id=2
> [4] FUNC_PROTO (anon) return=0 args=(void)
> [5] PTR (anon) type_id=4
>
> Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
Thanks for the fix.
Acked-by: Yonghong Song <yhs@xxxxxx>
> ---
> libbtf.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/libbtf.c b/libbtf.c
> index 478393b..c988d2a 100644
> --- a/libbtf.c
> +++ b/libbtf.c
> @@ -535,7 +535,7 @@ int32_t btf__add_func_proto(struct btf *btf, struct ftype *ftype,
>
> t.name_off = 0;
> t.info = BTF_INFO_ENCODE(BTF_KIND_FUNC_PROTO, 0, nr_params);
> - t.type = type_id_off + ftype->tag.type;
> + t.type = ftype->tag.type == 0 ? 0 : type_id_off + ftype->tag.type;
>
> ++btf->type_index;
> if (gobuffer__add(&btf->types, &t, sizeof(t)) >= 0) {
> @@ -552,9 +552,12 @@ int32_t btf__add_func_proto(struct btf *btf, struct ftype *ftype,
> /* add parameters */
> param_idx = 0;
> ftype__for_each_parameter(ftype, param) {
> + uint32_t param_type_id = param->tag.type == 0
> + ? 0
> + : type_id_off + param->tag.type;
> ++param_idx;
> if (btf__add_func_proto_param(btf, param->name,
> - type_id_off + param->tag.type,
> + param_type_id,
> param_idx == nr_params))
> return -1;
> }
>
