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 | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/tools/testing/selftests/bpf/bpf_helpers.h b/tools/testing/selftests/bpf/bpf_helpers.h index f804f210244e..e1a430101f40 100644 --- a/tools/testing/selftests/bpf/bpf_helpers.h +++ b/tools/testing/selftests/bpf/bpf_helpers.h @@ -501,4 +501,24 @@ 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)) + #endif -- 2.17.1
