Commit bdeeed34 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
Browse files

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



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: 5fbc2208 ("tools/libpf: Add offsetof/container_of macro in bpf_helpers.h")
Reported-by: default avatarLennart Poettering <lennart@poettering.net>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20230509065502.2306180-1-andrii@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent ee9fd0ac

tools/lib/bpf/bpf_helpers.h

+10 −5
Original line number Original line Diff line number Diff line
@@ -77,16 +77,21 @@ 
/*

/*

 * Helper macros to manipulate data structures

 * Helper macros to manipulate data structures

 */

 */

#ifndef offsetof



#define offsetof(TYPE, MEMBER)	((unsigned long)&((TYPE *)0)->MEMBER)

/* offsetof() definition that uses __builtin_offset() might not preserve field

#endif

 * offset CO-RE relocation properly, so force-redefine offsetof() using

#ifndef container_of

 * 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)				\

#define container_of(ptr, type, member)				\

	({							\

	({							\

		void *__mptr = (void *)(ptr);			\

		void *__mptr = (void *)(ptr);			\

		((type *)(__mptr - offsetof(type, member)));	\

		((type *)(__mptr - offsetof(type, member)));	\

	})

	})

#endif





/*

/*

 * Compiler (optimization) barrier.

 * Compiler (optimization) barrier.