Re: [PATCH v2 5/5] aarch64: Define __ASSUME_SYSCALL_NAMED_WORKS for Linux

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 25/03/23 11:08, Xi Ruoyao wrote:
> AAPCS treats the variable arguments same as named ones, and when each
> argument is an integer not wider than 8 bytes, the ith argument is in
> register xi (0 <= i < 8), or the stack slot at (sp + 8 * (i - 8))
> (i >= 8) no matter how many arguments are passed.  So we can define
> __ASSUME_SYSCALL_NAMED_WORKS to avoid unnecessary stack stores in the
> syscall wrappers caused by va_start.

This triggered a build failure on i686 patchwork buildbot [1].

[1] https://www.delorie.com/trybots/32bit/18431/

> ---
>  sysdeps/unix/sysv/linux/aarch64/kernel-features.h | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/sysdeps/unix/sysv/linux/aarch64/kernel-features.h b/sysdeps/unix/sysv/linux/aarch64/kernel-features.h
> index 3546f6de96..c39ff39da2 100644
> --- a/sysdeps/unix/sysv/linux/aarch64/kernel-features.h
> +++ b/sysdeps/unix/sysv/linux/aarch64/kernel-features.h
> @@ -21,3 +21,12 @@
>  
>  #undef __ASSUME_CLONE_DEFAULT
>  #define __ASSUME_CLONE_BACKWARDS 1
> +
> +/* Define this if the calling convention for passing x named arguments and y
> +   variable arguments is same as passing (x + y) named arguments, while each
> +   argument is either an integer of which the width is less than or equal to
> +   "long", or a pointer; and an argument can be fetched from the same register
> +   or the same offset from the stack pointer no matter how many (maybe zero)
> +   arguments are passed after it.  It avoids useless stack stores caused by
> +   usage of va_start.  */
> +#define __ASSUME_SYSCALL_NAMED_WORKS	1