Messages in this thread | | | Date | Wed, 2 Feb 2022 09:01:07 -0700 | From | Nathan Chancellor <> | Subject | Re: [PATCH] include: drop pointless __compiler_offsetof indirection |
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On Wed, Feb 02, 2022 at 11:21:47AM +0100, Rasmus Villemoes wrote: > (1) compiler_types.h is unconditionally included via an -include > flag (see scripts/Makefile.lib), and it defines __compiler_offsetof > unconditionally. So testing for definedness of __compiler_offsetof is > mostly pointless. > > (2) Every relevant compiler provides __builtin_offsetof (even sparse > has had that for 14 years), and if for whatever reason one would end > up picking up the poor man's fallback definition (C file compiler with > completely custom CFLAGS?), newer clang versions won't treat the > result as an Integer Constant Expression, so if used in place where > such is required (static initializer or static_assert), one would > get errors like > > t.c:11:16: error: static_assert expression is not an integral constant expression > t.c:11:16: note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression > t.c:4:33: note: expanded from macro 'offsetof' > #define offsetof(TYPE, MEMBER) ((size_t)&((TYPE *)0)->MEMBER) > > So just define offsetof unconditionally and directly in terms of > __builtin_offsetof. > > Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> --- > include/linux/compiler_types.h | 2 -- > include/linux/stddef.h | 6 +----- > 2 files changed, 1 insertion(+), 7 deletions(-) > > diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h > index 3c1795fdb568..83ee7f7ada5d 100644 > --- a/include/linux/compiler_types.h > +++ b/include/linux/compiler_types.h > @@ -137,8 +137,6 @@ struct ftrace_likely_data { > */ > #define __naked __attribute__((__naked__)) notrace > > -#define __compiler_offsetof(a, b) __builtin_offsetof(a, b) > - > /* > * Prefer gnu_inline, so that extern inline functions do not emit an > * externally visible function. This makes extern inline behave as per gnu89 > diff --git a/include/linux/stddef.h b/include/linux/stddef.h > index ca507bd5f808..929d67710cc5 100644 > --- a/include/linux/stddef.h > +++ b/include/linux/stddef.h > @@ -13,11 +13,7 @@ enum { > }; > > #undef offsetof > -#ifdef __compiler_offsetof > -#define offsetof(TYPE, MEMBER) __compiler_offsetof(TYPE, MEMBER) > -#else > -#define offsetof(TYPE, MEMBER) ((size_t)&((TYPE *)0)->MEMBER) > -#endif > +#define offsetof(TYPE, MEMBER) __builtin_offsetof(TYPE, MEMBER) > > /** > * sizeof_field() - Report the size of a struct field in bytes > -- > 2.31.1 >
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