Hi, On 12/4/18 2:26 AM, snyh wrote: > 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. Okay -- there's a lot of good info there (including your expertise/experience), that I've added to the commit message. I've applied the patch. Thanks! Michael > 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/ > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
