> On Jul 30, 2019, at 12:53 PM, Andrii Nakryiko <andriin@xxxxxx> wrote: > > Add BPF_CORE_READ macro used in tests to do bpf_core_read(), which > automatically captures offset relocation. > > Signed-off-by: Andrii Nakryiko <andriin@xxxxxx> > --- > tools/testing/selftests/bpf/bpf_helpers.h | 19 +++++++++++++++++++ > 1 file changed, 19 insertions(+) > > diff --git a/tools/testing/selftests/bpf/bpf_helpers.h b/tools/testing/selftests/bpf/bpf_helpers.h > index f804f210244e..81bc51293d11 100644 > --- a/tools/testing/selftests/bpf/bpf_helpers.h > +++ b/tools/testing/selftests/bpf/bpf_helpers.h > @@ -501,4 +501,23 @@ struct pt_regs; > (void *)(PT_REGS_FP(ctx) + sizeof(ip))); }) > #endif > > +/* > + * BPF_CORE_READ abstracts away bpf_probe_read() call and captures offset > + * relocation for source address using __builtin_preserve_access_index() > + * built-in, provided by Clang. > + * > + * __builtin_preserve_access_index() takes as an argument an expression of > + * taking an address of a field within struct/union. It makes compiler emit > + * a relocation, which records BTF type ID describing root struct/union and an > + * accessor string which describes exact embedded field that was used to take > + * an address. See detailed description of this relocation format and > + * semantics in comments to struct bpf_offset_reloc in libbpf_internal.h. > + * > + * This relocation allows libbpf to adjust BPF instruction to use correct > + * actual field offset, based on target kernel BTF type that matches original > + * (local) BTF, used to record relocation. > + */ > +#define BPF_CORE_READ(dst, src) \ > + bpf_probe_read(dst, sizeof(*src), __builtin_preserve_access_index(src)) We should use "sizeof(*(src))"
