[FFmpeg-devel] [PATCH v2] avutil/mips: Avoid instruction exception caused by gssqc1/gslqc1.

[Reimar Döffinger]

Is there a mips maintainer? otherwise:

On 24.07.2019, at 08:46, Shiyou Yin <yinshiyou-hf at loongson.cn> wrote:

> Ensure the address accesed by gssqc1/gslqc1 are 16-bits memory-aligned.
> ---
> libavcodec/mips/simple_idct_mmi.c | 2 +-
> libavutil/mips/mmiutils.h         | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/libavcodec/mips/simple_idct_mmi.c b/libavcodec/mips/simple_idct_mmi.c
> index 7f4bb74..73d797f 100644
> --- a/libavcodec/mips/simple_idct_mmi.c
> +++ b/libavcodec/mips/simple_idct_mmi.c
> @@ -39,7 +39,7 @@
> #define COL_SHIFT 20
> #define DC_SHIFT 3
> 
> -DECLARE_ALIGNED(8, const int16_t, W_arr)[46] = {
> +DECLARE_ALIGNED(16, const int16_t, W_arr)[46] = {
>     W4,  W2,  W4,  W6,
>     W1,  W3,  W5,  W7,
>     W4,  W6, -W4, -W2,

This should be fine, simply as it should not be possible for it to cause issues.

> diff --git a/libavutil/mips/mmiutils.h b/libavutil/mips/mmiutils.h
> index 05f6b31..bfa6d8b 100644
> --- a/libavutil/mips/mmiutils.h
> +++ b/libavutil/mips/mmiutils.h
> @@ -205,7 +205,7 @@
>  * backup register
>  */
> #define BACKUP_REG \
> -  double temp_backup_reg[8];                                    \
> +  double __attribute__ ((aligned (16))) temp_backup_reg[8];     \


I don't think we're supposed to use raw __attribute__ in FFmpeg, and for stack variables there can be even more issues.
Maybe check with what other code does...