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

On 12/31/2015 11:28 PM, 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.

That's correct svc does only support NR up to 255 directly.
For 256 and above %r1=NR and svc 0 is needed.
The svc 0 with setup r1 works for NR < 256, too.

So it seems all is fine, but we still need the patch to use the
socketcall interface until we can assume the direct socket syscalls are
always available. I'll repost the patch on the libc-stable interface
with the comment fixed, as I have been told in the meantimes it's a
better list for discussing about already released versions.
On s390x the direct socket syscalls were introduced with kernel 4.3.
Before 4.3, the socket syscalls were always done with c-files in sysdeps/unix/sysv/linux/.
The entries in syscalls.list were never used on s390x.

The upstream behaviour activates the direct socket calls if __LINUX_KERNEL_VERSION >= 0x040300. Otherwise the socketcall-wrapper-syscall is used.

If glibc is build on a system with kernel >= 4.3 and the entries in syscalls.list, then those direct syscalls are generated
and those aren't available on kernels < 4.3.

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