Commit 01340e31 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
Browse files

libbpf: Add BPF-side definitions of supported field relocation kinds 

Add enum definition for Clang's __builtin_preserve_field_info()
second argument (info_kind). Currently only byte offset and existence
are supported. Corresponding Clang changes introducing this built-in can
be found at [0]

  [0] https://reviews.llvm.org/D67980



Signed-off-by: default avatarAndrii Nakryiko <andriin@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191015182849.3922287-5-andriin@fb.com
parent 62561eb4

tools/lib/bpf/bpf_core_read.h

+23 −1
Original line number Diff line number Diff line
@@ -2,6 +2,28 @@ 
#ifndef __BPF_CORE_READ_H__

#define __BPF_CORE_READ_H__



/*

 * enum bpf_field_info_kind is passed as a second argument into

 * __builtin_preserve_field_info() built-in to get a specific aspect of

 * a field, captured as a first argument. __builtin_preserve_field_info(field,

 * info_kind) returns __u32 integer and produces BTF field relocation, which

 * is understood and processed by libbpf during BPF object loading. See

 * selftests/bpf for examples.

 */

enum bpf_field_info_kind {

	BPF_FIELD_BYTE_OFFSET = 0,	/* field byte offset */

	BPF_FIELD_EXISTS = 2,		/* field existence in target kernel */

};



/*

 * Convenience macro to check that field actually exists in target kernel's.

 * Returns:

 *    1, if matching field is present in target kernel;

 *    0, if no matching field found.

 */

#define bpf_core_field_exists(field)					    \

	__builtin_preserve_field_info(field, BPF_FIELD_EXISTS)



/*

 * bpf_core_read() abstracts away bpf_probe_read() call and captures offset

 * relocation for source address using __builtin_preserve_access_index()
@@ -12,7 +34,7 @@ 
 * 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.

 * semantics in comments to struct bpf_field_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