On 2026-08-02 09:06:59+0200, Magnus Lindholm wrote:
> 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
Ack.
> > + * - 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?
Good catch. We had miscompilations from clang in this case before.
So I'll fix this up to be on the safe side.
> 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 for the offer. For me Michael's Tested-by would be sufficient.
Thomas
