[Mesa-stable] [PATCH] ralloc: Make sure ralloc() allocations match malloc()'s alignment.

[Marek Olšák]

Reviewed-by: Marek Olšák <marek.olsak at amd.com>

Marek

On Wed, Mar 1, 2017 at 8:21 PM, Eric Anholt <eric at anholt.net> wrote:
> From: Jonas Pfeil <pfeiljonas at gmx.de>
>
> The header of ralloc needs to be aligned, because the compiler assumes
> that malloc returns will be aligned to 8/16 bytes depending on the
> platform, leading to degraded performance or alignment faults with ralloc.
>
> Fixes SIGBUS on Raspberry Pi at high optimization levels.
>
> This patch is not perfect for MSVC, as maybe in the future the alignment
> for the most demanding data type might change to more than 8.
>
> v2: Commit message reword/typo fix, and add a bigger explanation in the
>     code (by anholt)
>
> Signed-off-by: Jonas Pfeil <pfeiljonas at gmx.de>
> Cc: mesa-stable at lists.freedesktop.org
> ---
>  src/util/ralloc.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/src/util/ralloc.c b/src/util/ralloc.c
> index d5cc16766b10..03283de71802 100644
> --- a/src/util/ralloc.c
> +++ b/src/util/ralloc.c
> @@ -51,7 +51,18 @@ _CRTIMP int _vscprintf(const char *format, va_list argptr);
>
>  #define CANARY 0x5A1106
>
> -struct ralloc_header
> +/* Align the header's size so that ralloc() allocations will return with the
> + * same alignment as a libc malloc would have (8 on 32-bit GLIBC, 16 on
> + * 64-bit), avoiding performance penalities on x86 and alignment faults on
> + * ARM.
> + */
> +struct
> +#ifdef _MSC_VER
> + __declspec(align(8))
> +#else
> + __attribute__((aligned))
> +#endif
> +   ralloc_header
>  {
>  #ifdef DEBUG
>     /* A canary value used to determine whether a pointer is ralloc'd. */
> --
> 2.11.0
>
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