s390x: glibc widestring algorithms broken

Host environment

• Operating system: ArchLinux
• OS/kernel version: Linux ... 6.0.0-arch1-1 #1 SMP PREEMPT_DYNAMIC Tue, 04 Oct 2022 19:16:52 +0000 x86_64 GNU/Linux
• Architecture: x86_64
• QEMU flavor: qemu-s390x
• QEMU version: qemu-s390x version 7.1.0
• QEMU command line: qemu-s390x ./test -> output 0

/* test.c */
#include <wchar.h>
#include <stdio.h>

int main(void)
{
	printf("%ld\n", wcsspn(L"FOO", L"F"));
}

Emulated/Virtualized environment

• Operating system: user emulation
• OS/kernel version: user emulation
• Architecture: s390x
• Test program linked against glibc 2.35-0ubuntu3.1

Description of problem

Several wide-string functions from glibc are broken und qemu user emulation. Affected are at least: wcsbrk(), wcsspn() and wcscspn(). All of these are implemented in optimized assembler in glibc.

Unfortunately I don't have access to the real hardware to check the behavior there. But it would probably been detected by now. Also I don't know which instructions exactly don't work, as I don't have any knowledge about s390x assembler.

Steps to reproduce

1. Compile the test program above
2. Run the program
3. Output is 0, should be 1.