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libbpf bpf_helpers: Use __builtin_offsetof for offsetof 

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
This commit is contained in:
Ian Rogers 2020-07-19 23:17:41 -07:00 committed by Alexei Starovoitov
parent 94ad428df5
commit da7a35062b
1 changed files with 1 additions and 1 deletions
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2
tools/lib/bpf/bpf_helpers.h
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@ -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) \