The normal Alpha C ABI use a0~a5 to pass arguments and use v0 as the return value register. see here https://www2.cs.arizona.edu/projects/alto/Doc/local/alpha.register.html The syscall ABI use v0 as the trap number, a0~a5 to pass arguments and use a3 as a indicator(bool type) whether has a error occurred. We can also see the libc's syscall wrapper implements at here https://code.woboq.org/userspace/glibc/sysdeps/unix/sysv/linux/alpha/syscall.S.html The v0 is the normal used as return register, and we can see the return processing doesn't do anything about a0 which is the wrong register of currently syscall(2) description. p.s. I found this wrong description because I'm porting Go gc to a new CPU architecture which is similar to Alpha, And I use the wrong register at first, then I have inspect the kernel code and objdump to ensure the right syscall ABI. On Tue, Dec 4, 2018 at 5:16 AM Michael Kerrisk (man-pages) <mtk.manpages@xxxxxxxxx> wrote: > > [CC += Mike, original author of the text] > > On 12/3/18 4:07 AM, snyh wrote: > > alpha use v0 e.g. $0 as the return value register both in > > syscall abi and C abi. > > > > see also > > https://github.com/torvalds/linux/blob/master/arch/alpha/kernel/entry.S#L479 > > I need a little help here, probably in the form of a more > detailed commit message. Can you explain how one can verify > the point made in the patch? (I'm not wiser after following > the above link.) > > Thanks, > > Michael > > > diff --git a/man2/syscall.2 b/man2/syscall.2 > > index 3f4d64c..11e1416 100644 > > --- a/man2/syscall.2 > > +++ b/man2/syscall.2 > > @@ -181,7 +181,7 @@ and the register used to signal an error. > > l2 l2 l2 l2 l2 l. > > arch/ABI instruction syscall # retval error Notes > > _ > > -alpha callsys v0 a0 a3 [1] > > +alpha callsys v0 v0 a3 [1] > > arc trap0 r8 r0 - > > arm/OABI swi NR - a1 - [2] > > arm/EABI swi 0x0 r7 r0 - > > > > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/
