From: Ian Rogers <irogers@google.com>
Date: Sun, 19 Jul 2020 23:17:41 -0700
Subject: libbpf bpf_helpers: Use __builtin_offsetof for offsetof
Patch-mainline: v5.9-rc1
Git-commit: da7a35062bcccd3f67779a357065ba707b02ff2b
References: bsc#1177028

The non-builtin route for offsetof has a dependency on size_t from
stdlib.h/stdint.h that is undeclared and may break targets.
The offsetof macro in bpf_helpers may disable the same macro in other
headers that have a #ifdef offsetof guard. Rather than add additional
dependencies improve the offsetof macro declared here to use the
builtin that is available since llvm 3.7 (the first with a BPF backend).

Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200720061741.1514673-1-irogers@google.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)  ((size_t)&((TYPE *)0)->MEMBER)
+#define offsetof(TYPE, MEMBER)  __builtin_offsetof(TYPE, MEMBER)
 #endif
 #ifndef container_of
 #define container_of(ptr, type, member)				\