From: Yonghong Song <yhs@fb.com>
Date: Mon, 10 Aug 2020 20:08:52 -0700
Subject: libbpf: Do not use __builtin_offsetof for offsetof
Patch-mainline: v5.9-rc2
Git-commit: 63fe3fd393dc4e7ea3948e79947362ffbb0fd616
References: bsc#1177028

Commit 5fbc220862fc ("tools/libpf: Add offsetof/container_of macro
in bpf_helpers.h") added a macro offsetof() to get the offset of a
structure member:

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

In certain use cases, size_t type may not be available so
Commit da7a35062bcc ("libbpf bpf_helpers: Use __builtin_offsetof
for offsetof") changed to use __builtin_offsetof which removed
the dependency on type size_t, which I suggested.

But using __builtin_offsetof will prevent CO-RE relocation
generation in case that, e.g., TYPE is annotated with "preserve_access_info"
where a relocation is desirable in case the member offset is changed
in a different kernel version. So this patch reverted back to
the original macro but using "unsigned long" instead of "site_t".

Fixes: da7a35062bcc ("libbpf bpf_helpers: Use __builtin_offsetof for offsetof")
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/bpf/20200811030852.3396929-1-yhs@fb.com
Acked-by: Gary Lin <glin@suse.com>
---
 tools/lib/bpf/bpf_helpers.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -40,7 +40,7 @@
  * Helper macro to manipulate data structures
  */
 #ifndef offsetof
-#define offsetof(TYPE, MEMBER)  __builtin_offsetof(TYPE, MEMBER)
+#define offsetof(TYPE, MEMBER)	((unsigned long)&((TYPE *)0)->MEMBER)
 #endif
 #ifndef container_of
 #define container_of(ptr, type, member)				\