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libbpf: Add support for relocatable bitfields

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Add support for the new field relocation kinds, necessary to support
relocatable bitfield reads. Provide macro for abstracting necessary code doing
full relocatable bitfield extraction into u64 value. Two separate macros are
provided:
- BPF_CORE_READ_BITFIELD macro for direct memory read-enabled BPF programs
(e.g., typed raw tracepoints). It uses direct memory dereference to extract
bitfield backing integer value.
- BPF_CORE_READ_BITFIELD_PROBED macro for cases where bpf_probe_read() needs
to be used to extract same backing integer value.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20191101222810.1246166-3-andriin@fb.com
This commit is contained in:
Andrii Nakryiko
2019-11-01 15:28:07 -07:00
committed by Andrii Nakryiko
parent 09cd9ff2db
commit 4438972ccc
3 changed files with 227 additions and 60 deletions
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4
src/libbpf_internal.h
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@@ -158,7 +158,11 @@ struct bpf_line_info_min {
*/
enum bpf_field_info_kind {
BPF_FIELD_BYTE_OFFSET = 0, /* field byte offset */
BPF_FIELD_BYTE_SIZE = 1,
BPF_FIELD_EXISTS = 2, /* field existence in target kernel */
BPF_FIELD_SIGNED = 3,
BPF_FIELD_LSHIFT_U64 = 4,
BPF_FIELD_RSHIFT_U64 = 5,
};
/* The minimum bpf_field_reloc checked by the loader