This is a note to let you know that I've just added the patch titled
libbpf: fix offsetof() and container_of() to work with CO-RE
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
libbpf-fix-offsetof-and-container_of-to-work-with-co.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 8a7a9f3fa7e6f0c1bec40f4048358a1cde9714d0
Author: Andrii Nakryiko <andrii@xxxxxxxxxx>
Date: Mon May 8 23:55:02 2023 -0700
libbpf: fix offsetof() and container_of() to work with CO-RE
[ 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@xxxxxxxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Acked-by: Yonghong Song <yhs@xxxxxx>
Link: https://lore.kernel.org/r/20230509065502.2306180-1-andrii@xxxxxxxxxx
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index 72b251110c4d7..1c389b0f5499a 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -42,16 +42,21 @@
/*
* Helper macro 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
