Re: [PATCH v2] tools/nolibc: add support for Alpha

Hi Thomas,

On Wed, Jul 22, 2026 at 3:28 AM Thomas Weißschuh <[email protected]> wrote:

> + * Syscalls for Alpha:
> + *   - registers are 64-bit
> + *   - syscall number is passed in $0/v0
> + *   - the system call is performed by calling callsys
> + *   - syscall return comes in $0/v0, error flag in $19/a4

typo in comment ? should be:
 syscall return comes in $0/v0, error flag in $19/a3

> + *   - arguments are passed in $16/a0 to $21/a5
> + *   - GCC does not support symbol register names
> + */


> +#define __nolibc_syscall5(num, arg1, arg2, arg3, arg4, arg5)                  \
> +({                                                                            \
> +       register long _num __asm__ ("$0") = (num);                            \
> +       register long _err __asm__ ("$19");                                   \
> +       register long _arg1 __asm__ ("$16") = (long)(arg1);                   \
> +       register long _arg2 __asm__ ("$17") = (long)(arg2);                   \
> +       register long _arg3 __asm__ ("$18") = (long)(arg3);                   \
> +       register long _arg4 __asm__ ("$19") = (long)(arg4);                   \
> +       register long _arg5 __asm__ ("$20") = (long)(arg5);                   \
> +                                                                              \
> +       __asm__ volatile (                                                    \
> +               "callsys"                                                     \
> +               : "+r"(_num), "=r"(_err)                                      \
> +               : "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5)  \
> +               : _NOLIBC_SYSCALL_CLOBBERLIST, "$21"                          \
> +       );                                                                    \
> +       _err ? -_num : _num;                                                  \
> +})

One observation, although I am not an expert on GCC inline-assembly constraints:
in the four- through six-argument wrappers, $19/a3 contains the fourth
argument on
entry and the error indicator on return. Would using a single read/write operand
for $19, similar to the handling of $0, make that transition clearer?

Michael’s successful testing on both XP1000 and ES45 also shows that the current
implementation works correctly on real hardware, so I do not consider
changing the
operand representation a requirement for v3. From my side, addressing the $19/a4
comment typo, together with the "TASK_SIZEi" typo already noted by Willy,
would be sufficient.

Michael’s testing should be sufficient, but I also have access to Alpha hardware
and would be happy to assist with any additional testing if useful.

Thanks alot for taking the time to do this.

Regards,
Magnus