selftests/bpf: add BPF_CORE_READ relocatable read macro (2dc26d5a) · Commits · 戴 / test

tools/testing/selftests/bpf/bpf_helpers.h

+20 −0

Original line number	Diff line number	Diff line
		@@ -504,4 +504,24 @@ 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