Re: [FFmpeg-devel] [PATCH 1/2] aarch64: Simplify the linux runtime cpu detection code

[Sean McGovern <gseanmcg@gmail.com>]

On Tue, Oct 24, 2023, 08:23 Martin Storsjö <martin@martin.st> wrote:

> Skip doing the whole getauxval(AT_HWCAP) if HWCAP_CPUID isn't
> defined.
> ---
>  libavutil/aarch64/cpu.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
>
> diff --git a/libavutil/aarch64/cpu.c b/libavutil/aarch64/cpu.c
> index bd780e8591..2b50c426bc 100644
> --- a/libavutil/aarch64/cpu.c
> +++ b/libavutil/aarch64/cpu.c
> @@ -30,11 +30,9 @@
>  static int detect_flags(void)
>  {
>      int flags = 0;
> -    unsigned long hwcap;
> -
> -    hwcap = getauxval(AT_HWCAP);
>
>  #if defined(HWCAP_CPUID)
> +    unsigned long hwcap = getauxval(AT_HWCAP);
>      // We can check for DOTPROD and I8MM using HWCAP_ASIMDDP and
>      // HWCAP2_I8MM too, avoiding to read the CPUID registers (which
> triggers
>      // a trap, handled by the kernel). However the HWCAP_* defines for
> these
> @@ -53,8 +51,6 @@ static int detect_flags(void)
>          if (((tmp >> 52) & 0xf) == 0x1)
>              flags |= AV_CPU_FLAG_I8MM;
>      }
> -#else
> -    (void)hwcap;
>  #endif
>
>      return flags;
> --
> 2.34.1
>
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Good call, and LGTM.

-- Sean McGovern

>
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