From: Andrii Nakryiko andrii@kernel.org
[ Upstream commit bdeeed3498c7871c17465bb4f11d1bc67f9098af ]
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: 5fbc220862fc ("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 Signed-off-by: Sasha Levin sashal@kernel.org --- tools/lib/bpf/bpf_helpers.h | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h index b9987c3efa3c4..956b57d02eb9a 100644 --- a/tools/lib/bpf/bpf_helpers.h +++ b/tools/lib/bpf/bpf_helpers.h @@ -72,16 +72,21 @@ /* * 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
/* * Helper macro to throw a compilation error if __bpf_unreachable() gets