Re: [PATCH v5 2/3] aarch64: Set the syscall register right before doing the syscall.

[Szabolcs Nagy <szabolcs.nagy@arm.com>]

The 04/19/2023 09:58, Joe Simmons-Talbott via Libc-alpha wrote:
> --- a/sysdeps/unix/sysv/linux/aarch64/sysdep.h
> +++ b/sysdeps/unix/sysv/linux/aarch64/sysdep.h
> @@ -168,15 +168,26 @@
>  # define HAVE_CLONE3_WRAPPER		1
>  
>  # undef INTERNAL_SYSCALL_RAW
> -# define INTERNAL_SYSCALL_RAW(name, nr, args...)		\
> -  ({ long _sys_result;						\
> -     {								\
> -       LOAD_ARGS_##nr (args)					\
> -       register long _x8 asm ("x8") = (name);			\
> -       asm volatile ("svc	0	// syscall " # name     \
> -		     : "=r" (_x0) : "r"(_x8) ASM_ARGS_##nr : "memory");	\
> -       _sys_result = _x0;					\
> -     }								\
> +# define INTERNAL_SYSCALL_RAW(name, nr, args...)			\
> +  ({ long _sys_result;							\
> +     {									\
> +       LOAD_ARGS_##nr (args)						\
> +       if (__builtin_constant_p(name))					\
> +         asm volatile ("mov	x8, %1	// syscall " # name "\n"	\
> +		       "svc	0"					\
> +                       : "=r" (_x0)					\
> +		       : "i" (name) ASM_ARGS_##nr			\
> +		       : "x8", "memory");				\
> +       else								\
> +         {								\
> +           register long _x8 asm ("x8") = (name);			\
> +           asm volatile ("svc	0\n\t"					\

why \n\t ?

i don't think that's needed.

> +		         : "=r" (_x0)					\
> +		         : "r"(_x8) ASM_ARGS_##nr			\
> +		         : "memory");					\
> +         }								\
> +       _sys_result = _x0;						\
> +     }									\
>       _sys_result; })
>  
>  # undef INTERNAL_SYSCALL