Re: [PATCH 5/7] tools/nolibc: handle 64-bit system call arguments on MIPS N32

[David Laight <david.laight.linux@gmail.com>]

On Sat, 18 Apr 2026 12:20:00 +0200
Thomas Weißschuh <linux@weissschuh.net> wrote:

> The N32 system call ABI expects 64-bit values directly in registers.
> This does not work on nolibc currently, as a 'long' is only 32 bits
> wide. Switch the system call wrappers to use 'long long' instead which
> can handle 64-bit values on N32. As on N64 'long' and 'long long' are
> the same, this does not change the behavior there.
> 
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---
>  tools/include/nolibc/arch-mips.h | 94 +++++++++++++++++++++-------------------
>  1 file changed, 49 insertions(+), 45 deletions(-)
> 
> diff --git a/tools/include/nolibc/arch-mips.h b/tools/include/nolibc/arch-mips.h
> index bb9d580ea1b1..557ef34d9df8 100644
> --- a/tools/include/nolibc/arch-mips.h
> +++ b/tools/include/nolibc/arch-mips.h
> @@ -55,6 +55,8 @@
>  #define _NOLIBC_SYSCALL_STACK_RESERVE "addiu $sp, $sp, -32\n"
>  #define _NOLIBC_SYSCALL_STACK_UNRESERVE "addiu $sp, $sp, 32\n"
>  
> +#define _NOLIBC_SYSCALL_REG register long
> +
>  #else /* _ABIN32 || _ABI64 */
>  
>  /* binutils, GCC and clang disagree about register aliases, use numbers instead. */
> @@ -66,12 +68,14 @@
>  #define _NOLIBC_SYSCALL_STACK_RESERVE
>  #define _NOLIBC_SYSCALL_STACK_UNRESERVE
>  
> +#define _NOLIBC_SYSCALL_REG register long long
> +
>  #endif /* _ABIO32 */

Since you need to use a #define, did you think about:
#define _NOLIBC_SYSCALL_REG(var, reg) register long long var __asm__ (reg)
to shorten the lines and the repetitive pattern.

>  
>  #define __nolibc_syscall0(num)                                                \
>  ({                                                                            \
> -	register long _num __asm__ ("v0") = (num);                            \
> -	register long _arg4 __asm__ ("a3");                                   \
> +	_NOLIBC_SYSCALL_REG _num __asm__ ("v0")  = (num);                     \
> +	_NOLIBC_SYSCALL_REG _arg4 __asm__ ("a3");                             \

	__NOLIBC_SYSCALL_REG(_num, "v0") = (num);
	__NOLIBC_SYSCALL_REG(_arg4, "a3");

...

	David