PATCH: Define MALLOC_ALIGNMENT as 16 for x32

[H.J. Lu]

On Tue, May 15, 2012 at 10:04 AM, Roland McGrath <roland@hack.frob.com> wrote:
> I don't think that's the right way to do it.
> How about this instead?
>
> diff --git a/malloc/malloc.c b/malloc/malloc.c
> index 79cdc52..0000000 100644
> --- a/malloc/malloc.c
> +++ b/malloc/malloc.c
> @@ -337,16 +337,20 @@ __malloc_assert (const char *assertion,
>
>
>  #ifndef MALLOC_ALIGNMENT
> -/* XXX This is the correct definition.  It differs from 2*SIZE_SZ only on
> -   powerpc32.  For the time being, changing this is causing more
> -   compatibility problems due to malloc_get_state/malloc_set_state than
> -   will returning blocks not adequately aligned for long double objects
> -   under -mlong-double-128.
> +# if !SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_16)
> +/* This is the correct definition when there is no past ABI to constrain it.
>
> -#define MALLOC_ALIGNMENT       (2 * SIZE_SZ < __alignof__ (long double) \
> -                               ? __alignof__ (long double) : 2 * SIZE_SZ)
> -*/
> -#define MALLOC_ALIGNMENT       (2 * SIZE_SZ)
> +   Among configurations with a past ABI constraint, it differs from
> +   2*SIZE_SZ only on powerpc32.  For the time being, changing this is
> +   causing more compatibility problems due to malloc_get_state and
> +   malloc_set_state than will returning blocks not adequately aligned for
> +   long double objects under -mlong-double-128.  */
> +
> +#  define MALLOC_ALIGNMENT       (2 * SIZE_SZ < __alignof__ (long double) \
> +                                 ? __alignof__ (long double) : 2 * SIZE_SZ)
> +# else
> +#  define MALLOC_ALIGNMENT       (2 * SIZE_SZ)
> +# endif
>  #endif
>
>  /* The corresponding bit mask value */

Will it change malloc alignment for i386? X32 MALLOC_ALIGNMENT == 16
is specified in x32 psABI. Malloc doesn't need to guess it.  We should just
define x32 MALLOC_ALIGNMENT to 16.

-- 
H.J.