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SubjectRe: [PATCH] libbpf bpf_helpers: Use __builtin_offsetof for offsetof if available
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On 7/17/20 12:23 AM, Ian Rogers wrote:
> 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 if available.
>
> Signed-off-by: Ian Rogers <irogers@google.com>

Thanks. I didn't pay attention to __builtin_offsetof() and clearly
it is preferred. Ack the change with a nit below.

Acked-by: Yonghong Song <yhs@fb.com>

> ---
> tools/lib/bpf/bpf_helpers.h | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
> index a510d8ed716f..ed2ac74fc515 100644
> --- a/tools/lib/bpf/bpf_helpers.h
> +++ b/tools/lib/bpf/bpf_helpers.h
> @@ -40,8 +40,12 @@
> * Helper macro to manipulate data structures
> */
> #ifndef offsetof
> +#if __has_builtin(__builtin_offsetof)
> +#define offsetof(TYPE, MEMBER) __builtin_offsetof(TYPE, MEMBER)

The __builtin_offsetof is actually available at least since llvm 3.7,
so it is safe to use it always.

> +#else
> #define offsetof(TYPE, MEMBER) ((size_t)&((TYPE *)0)->MEMBER)
> #endif
> +#endif
> #ifndef container_of
> #define container_of(ptr, type, member) \
> ({ \
>

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