[PATCH] AArch64: Remove prefer_sve_ifuncs

[Yury Khrustalev]

On Mon, Mar 16, 2026 at 02:38:52PM +0000, Wilco Dijkstra wrote:
> 
> Remove the prefer_sve_ifuncs CPU feature since it was intended for older
> kernels. Current distros all use modern Linux kernels with improved support for
> SVE save/restore, making this check redundant.
> 
> OK for commit?

Seems OK to me, however please see one comment below.

>
> ...
> diff --git a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
> index 15aed15a667e89abd2790a22a319a8a6aaecba02..1e4f8a86b1017e5682aec29e975061a31160af46 100644
> --- a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
> +++ b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
> @@ -65,46 +65,6 @@ get_midr_from_mcpu (const struct tunable_str_t *mcpu)
>    return UINT64_MAX;
>  }
>  
> -#if __LINUX_KERNEL_VERSION < 0x060200
> -
> -/* Return true if we prefer using SVE in string ifuncs.  Old kernels disable
> -   SVE after every system call which results in unnecessary traps if memcpy
> -   uses SVE.  This is true for kernels between 4.15.0 and before 6.2.0, except
> -   for 5.14.0 which was patched.  For these versions return false to avoid using
> -   SVE ifuncs.
> -   Parse the kernel version into a 24-bit kernel.major.minor value without
> -   calling any library functions.  If uname() is not supported or if the version
> -   format is not recognized, assume the kernel is modern and return true.  */
> -
> -static inline bool
> -prefer_sve_ifuncs (void)
> -{
> -  struct utsname buf;
> -  const char *p = &buf.release[0];
> -  int kernel = 0;
> -  int val;
> -
> -  if (__uname (&buf) < 0)
> -    return true;
> -
> -  for (int shift = 16; shift >= 0; shift -= 8)
> -    {
> -      for (val = 0; *p >= '0' && *p <= '9'; p++)
> -	val = val * 10 + *p - '0';
> -      kernel |= (val & 255) << shift;
> -      if (*p++ != '.')
> -	break;
> -    }
> -
> -  if (kernel >= 0x060200 || kernel == 0x050e00)
> -    return true;
> -  if (kernel >= 0x040f00)
> -    return false;
> -  return true;
> -}
> -
> -#endif
> -
>  static inline void
>  init_cpu_features (struct cpu_features *cpu_features)
>  {
> @@ -171,13 +131,6 @@ init_cpu_features (struct cpu_features *cpu_features)
>    /* Check if SVE is supported.  */
>    cpu_features->sve = GLRO (dl_hwcap) & HWCAP_SVE;
>  
> -  cpu_features->prefer_sve_ifuncs = cpu_features->sve;

What if cpu_features->sve is false?

> -
> -#if __LINUX_KERNEL_VERSION < 0x060200
> -  if (cpu_features->sve)
> -    cpu_features->prefer_sve_ifuncs = prefer_sve_ifuncs ();
> -#endif
> -
>    /* Check if MOPS is supported.  */
>    cpu_features->mops = GLRO (dl_hwcap2) & HWCAP2_MOPS;
>  
>