Re: [PATCH 2/2] Use C11 _Alignas on scratch_buffer internal buffer

[Florian Weimer <fweimer at redhat dot com>]

On 09/18/2017 04:42 PM, Adhemerval Zanella wrote:
> Checked on x86_64-linux-gnu.
>
> 	* include/scratch_buffer.h (scratch_buffer): Use C11 _Alignas on
> 	__space field definition if compiler supports it.
> ---
>   ChangeLog                | 3 +++
>   include/scratch_buffer.h | 5 +++++
>   2 files changed, 8 insertions(+)
>
> diff --git a/include/scratch_buffer.h b/include/scratch_buffer.h
> index bb04662..2e0c8b5 100644
> --- a/include/scratch_buffer.h
> +++ b/include/scratch_buffer.h
> @@ -60,13 +60,18 @@
>   #include <stdbool.h>
>   #include <stddef.h>
>   #include <stdlib.h>
> +#include <stdalign.h>
>   
>   /* Scratch buffer.  Must be initialized with scratch_buffer_init
>      before its use.  */
>   struct scratch_buffer {
>     void *data;    /* Pointer to the beginning of the scratch area.  */
>     size_t length; /* Allocated space at the data pointer, in bytes.  */
> +#if __alignas_is_defined
> +  _Alignas (max_align_t) char __space[1024];
> +#else
>     max_align_t __space[(1023 + sizeof (max_align_t)) / sizeof (max_align_t)];
> +#endif

Okay, I think.

(Richard has spoken: The code with max_align_t is okay as well as far as 
GCC is concerned.  But I think it's useful to keep the initial buffer 
size in sync on all architectures to reduce variance, so please push 
this change.)

Thanks,
Florian.