On Wed, Jul 24, 2019 at 12:28 PM Andrii Nakryiko <andriin@xxxxxx> wrote:
>
> Add support for BPF CO-RE offset relocations. Add section/record
> iteration macros for .BTF.ext. These macro are useful for iterating over
> each .BTF.ext record, either for dumping out contents or later for BPF
> CO-RE relocation handling.
>
> To enable other parts of libbpf to work with .BTF.ext contents, moved
> a bunch of type definitions into libbpf_internal.h.
>
> Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
> ---
[...]
> + *
> + * Example to provide a better feel.
> + *
> + * struct sample {
> + * int a;
> + * struct {
> + * int b[10];
> + * };
> + * };
> + *
> + * struct sample *s = ...;
> + * int x = &s->a; // encoded as "0:0" (a is field #0)
> + * int y = &s->b[5]; // encoded as "0:1:5" (b is field #1, arr elem #5)
This should be "0:1:0:5", actually. Anon struct is field #1 in BTF, b
is field #0 inside that anon struct + array index 5.
Will update it locally and incorporate into next version once the rest
of patch set is reviewed.
> + * int z = &s[10]->b; // encoded as "10:1" (ptr is used as an array)
> + *
> + * type_id for all relocs in this example will capture BTF type id of
> + * `struct sample`.
> + *
> + * [0] https://llvm.org/docs/LangRef.html#getelementptr-instruction
> + */
> +struct bpf_offset_reloc {
> + __u32 insn_off;
> + __u32 type_id;
> + __u32 access_str_off;
> +};
> +
> #endif /* __LIBBPF_LIBBPF_INTERNAL_H */
> --
> 2.17.1
>
