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libbpf: Complete field-based CO-RE helpers with field offset helper

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Add bpf_core_field_offset() helper to complete field-based CO-RE
helpers. This helper can be useful for feature-detection and for some
more advanced cases of field reading (e.g., reading flexible array members).

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220509004148.1801791-6-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2022-05-08 17:41:44 -07:00 committed by Daniel Borkmann
parent 2a4ca46b7d
commit 7715f549a9
1 changed files with 12 additions and 0 deletions
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12
tools/lib/bpf/bpf_core_read.h
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@ -143,6 +143,18 @@ enum bpf_enum_value_kind {
#define bpf_core_field_size(field...) \
__builtin_preserve_field_info(___bpf_field_ref(field), BPF_FIELD_BYTE_SIZE)
/*
* Convenience macro to get field's byte offset.
*
* Supports two forms:
* - field reference through variable access:
* bpf_core_field_offset(p->my_field);
* - field reference through type and field names:
* bpf_core_field_offset(struct my_type, my_field).
*/
#define bpf_core_field_offset(field...) \
__builtin_preserve_field_info(___bpf_field_ref(field), BPF_FIELD_BYTE_OFFSET)
/*
* Convenience macro to get BTF type ID of a specified type, using a local BTF
* information. Return 32-bit unsigned integer with type ID from program's own