[PATCH v3] RISC-V: add multiarch RVV support for memcpy using FMV IFUNC

[Darius Rad]

On Mon, Jan 20, 2025 at 11:26:47AM +0800, daichengrong@iscas.ac.cn wrote:
> From: daichengrong <daichengrong@iscas.ac.cn>
> 
> This patch introduces vector support for memcpy with IFUNC.
> The implementation select the RVV optimized memcpy version via hwprobe on kernel with RVV enabled.
> 

[...]

> diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c b/sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c
> index 8544f5402a..105c837101 100644
> --- a/sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c
> +++ b/sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c
> @@ -32,11 +32,16 @@ extern __typeof (__redirect_memcpy) __libc_memcpy;
>  
>  extern __typeof (__redirect_memcpy) __memcpy_generic attribute_hidden;
>  extern __typeof (__redirect_memcpy) __memcpy_noalignment attribute_hidden;
> +extern __typeof (__redirect_memcpy) __memcpy_vector attribute_hidden;
>  
>  static inline __typeof (__redirect_memcpy) *
>  select_memcpy_ifunc (uint64_t dl_hwcap, __riscv_hwprobe_t hwprobe_func)
>  {
>    unsigned long long int v;
> +  if (__riscv_hwprobe_one (hwprobe_func, RISCV_HWPROBE_KEY_IMA_EXT_0, &v) == 0
> +      && (v & RISCV_HWPROBE_IMA_V) == RISCV_HWPROBE_IMA_V)
> +    return __memcpy_vector;
> +

Availability of vector should probably be determined with dl_hwcap, rather
than hwprobe_func, since vector may not be enabled (by prctl).

>    if (__riscv_hwprobe_one (hwprobe_func, RISCV_HWPROBE_KEY_CPUPERF_0, &v) == 0
>        && (v & RISCV_HWPROBE_MISALIGNED_MASK) == RISCV_HWPROBE_MISALIGNED_FAST)
>      return __memcpy_noalignment;