[ruby-core:111826] Re: [PATCH] fiddle: Use C11 _Alignof to define ALIGN_OF when possible

Hi,

Could you open a pull request for this?
https://github.com/ruby/fiddle/pulls

Thanks,
-- 
kou

In <[e-mail]>
  "[ruby-core:111823] [PATCH] fiddle: Use C11 _Alignof to define ALIGN_OF when possible" on Sun, 15 Jan 2023 20:02:42 -0800,
  Khem Raj via ruby-core <[e-mail]> wrote:

> WG14 N2350 made very clear that it is an UB having type definitions
> within "offsetof" [1]. This patch enhances the implementation of macro
> ALIGN_OF to use builtin "_Alignof" to avoid undefined behavior
> when using std=c11 or newer
> 
> clang 16+ has started to flag this [2]
> 
> Fixes build when using -std >= gnu11 and using clang16+
> 
> Older compilers gcc < 4.9 or clang < 8 has buggy _Alignof even though it
> may support C11, exclude those compiler versions
> 
> [1] https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm
> [2] https://reviews.llvm.org/D133574
> 
> Signed-off-by: Khem Raj <[e-mail]>
> ---
>  ext/fiddle/fiddle.h | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/ext/fiddle/fiddle.h b/ext/fiddle/fiddle.h
> index 10eb9ce..ffb395e 100644
> --- a/ext/fiddle/fiddle.h
> +++ b/ext/fiddle/fiddle.h
> @@ -196,7 +196,17 @@
>  #endif
>  #define TYPE_UINTPTR_T (-TYPE_INTPTR_T)
>  
> -#define ALIGN_OF(type) offsetof(struct {char align_c; type align_x;}, align_x)
> +/* GCC releases before GCC 4.9 had a bug in _Alignof.  See GCC bug 52023
> +   <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>.
> +   clang versions < 8.0.0 have the same bug.  */
> +#if (!defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 \
> +     || (defined __GNUC__ && __GNUC__ < 4 + (__GNUC_MINOR__ < 9) \
> +         && !defined __clang__) \
> +     || (defined __clang__ && __clang_major__ < 8))
> +# define ALIGN_OF(type) offsetof(struct {char align_c; type align_x;}, align_x)
> +#else
> +# define ALIGN_OF(type) _Alignof(type)
> +#endif
>  
>  #define ALIGN_VOIDP  ALIGN_OF(void*)
>  #define ALIGN_CHAR   ALIGN_OF(char)
> -- 
> 2.39.0
> 
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