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libbpf: fix offsetof() and container_of() to work with CO-RE

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It seems like __builtin_offset() doesn't preserve CO-RE field
relocations properly. So if offsetof() macro is defined through
__builtin_offset(), CO-RE-enabled BPF code using container_of() will be
subtly and silently broken.

To avoid this problem, redefine offsetof() and container_of() in the
form that works with CO-RE relocations more reliably.

Fixes: 5fbc220862 ("tools/libpf: Add offsetof/container_of macro in bpf_helpers.h")
Reported-by: Lennart Poettering <lennart@poettering.net>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20230509065502.2306180-1-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Andrii Nakryiko 2023-05-08 23:55:02 -07:00 committed by Alexei Starovoitov
parent ee9fd0ac30
commit bdeeed3498
1 changed files with 10 additions and 5 deletions
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15
tools/lib/bpf/bpf_helpers.h
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@ -77,16 +77,21 @@
/*
* Helper macros to manipulate data structures
*/
#ifndef offsetof
#define offsetof(TYPE, MEMBER) ((unsigned long)&((TYPE *)0)->MEMBER)
#endif
#ifndef container_of
/* offsetof() definition that uses __builtin_offset() might not preserve field
* offset CO-RE relocation properly, so force-redefine offsetof() using
* old-school approach which works with CO-RE correctly
*/
#undef offsetof
#define offsetof(type, member) ((unsigned long)&((type *)0)->member)
/* redefined container_of() to ensure we use the above offsetof() macro */
#undef container_of
#define container_of(ptr, type, member) \
({ \
void *__mptr = (void *)(ptr); \
((type *)(__mptr - offsetof(type, member))); \
})
#endif
/*
* Compiler (optimization) barrier.