Re: [FFmpeg-devel] [PATCH] avutil: [LA] use getauxval to do runtime check.

From: Steven Liu <lingjiujianke@gmail.com>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH] avutil: [LA] use getauxval to do runtime check.
Date: Thu, 23 Feb 2023 15:48:02 +0800
Message-ID: <CADxeRwmUf=BUT-8xuKe8wNDcuNLEa-_1zvu-EBu-nO_Am4tYkw@mail.gmail.com> (raw)
In-Reply-To: <20230214122556.24384-1-yinshiyou-hf@loongson.cn>

Shiyou Yin <yinshiyou-hf@loongson.cn> 于2023年2月14日周二 20:26写道：
>
> Replace cpucfg with getauxval to avoid crash in case of
> some processor capabilities are not supportted by kernel used.
> ---
>  libavutil/loongarch/cpu.c | 24 ++++++++----------------
>  1 file changed, 8 insertions(+), 16 deletions(-)
>
> diff --git a/libavutil/loongarch/cpu.c b/libavutil/loongarch/cpu.c
> index e4b240bc44..cad8504fde 100644
> --- a/libavutil/loongarch/cpu.c
> +++ b/libavutil/loongarch/cpu.c
> @@ -21,26 +21,18 @@
>
>  #include <stdint.h>
>  #include "cpu.h"
> +#include <sys/auxv.h>
>
> -#define LOONGARCH_CFG2 0x2
> -#define LOONGARCH_CFG2_LSX    (1 << 6)
> -#define LOONGARCH_CFG2_LASX   (1 << 7)
> -
> -static int cpu_flags_cpucfg(void)
> +#define LA_HWCAP_LSX    (1<<4)
> +#define LA_HWCAP_LASX   (1<<5)
> +static int cpu_flags_getauxval(void)
>  {
>      int flags = 0;
> -    uint32_t cfg2 = 0;
> -
> -    __asm__ volatile(
> -        "cpucfg %0, %1 \n\t"
> -        : "+&r"(cfg2)
> -        : "r"(LOONGARCH_CFG2)
> -    );
> +    int flag  = (int)getauxval(AT_HWCAP);
>
> -    if (cfg2 & LOONGARCH_CFG2_LSX)
> +    if (flag & LA_HWCAP_LSX)
>          flags |= AV_CPU_FLAG_LSX;
> -
> -    if (cfg2 & LOONGARCH_CFG2_LASX)
> +    if (flag & LA_HWCAP_LASX)
>          flags |= AV_CPU_FLAG_LASX;
>
>      return flags;
> @@ -49,7 +41,7 @@ static int cpu_flags_cpucfg(void)
>  int ff_get_cpu_flags_loongarch(void)
>  {
>  #if defined __linux__
> -    return cpu_flags_cpucfg();
> +    return cpu_flags_getauxval();
>  #else
>      /* Assume no SIMD ASE supported */
>      return 0;
> --
> 2.20.1
>
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LGTM

Thanks
Steven
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