Re: [PATCH-for-2.21-and-2.22] s390-64: remove socketcall syscalls

["Dmitry V. Levin" <ldv at altlinux dot org>]

On Fri, Jan 01, 2016 at 11:05:04PM -0500, Mike Frysinger wrote:
> On 31 Dec 2015 23:28, Aurelien Jarno wrote:
> > I have found some times to investigate. It seems there is no issue, my
> > bad. I just discovered that on s390x, syscalls numbers above 256 are
> > actually a a call to syscall 0 with the syscall number passed in
> > register %r1. My version of strace was not aware of the new syscalls 
> > and presented them as syscall setup(). Sorry for the false alert.
> 
> is this a bug in strace ?  does it not handle `svc 0` insns correctly ?
> if so, we should fix that.  i assumed the kernel would put the correct
> NR into the r1 register regardless of how the syscall was invoked, but
> maybe i'm being naive.

It's https://bugs.debian.org/485979

strace assumes that syscall number on s390/s390x is available in %r2,
which is correct both for "svc NR" and "svc 0 %r1=NR" methods unless
NR >= kernel's NR_syscalls.  In the latter case, %r2 is set to 0
but the original value that was stored in %r1 is also available
for a tracer.

I've pushed a fix (strace commit v4.11-159-g1763fa5) for this
longstanding issue.


-- 
ldv

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