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authorAndrii Nakryiko <andrii@kernel.org>2023-05-08 23:55:02 -0700
committerAlexei Starovoitov <ast@kernel.org>2023-05-12 12:05:21 -0700
commitbdeeed3498c7871c17465bb4f11d1bc67f9098af (patch)
treeb221e4b559bc7a642dd03266074cdb91ecdabbd7
parentee9fd0ac3017c4313be91a220a9ac4c99dde7ad4 (diff)
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: 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>
-rw-r--r--tools/lib/bpf/bpf_helpers.h15
1 files changed, 10 insertions, 5 deletions
diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index 929a3baca8ef..bbab9ad9dc5a 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -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.