New subject: [Bug 58420] Wine crashes when running msys2 iff CPU's PKU/PKRU feature is enabled

27 Jun 2025


      http://bugs.winehq.org/show_bug.cgi?id=58420
Bug ID: 58420
           Summary: Wine crashes when running msys2 iff CPU's PKU/PKRU
                    feature is enabled
           Product: Wine
           Version: unspecified
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: minor
          Priority: P2
         Component: -unknown
          Assignee: wine-bugs@winehq.org
          Reporter: pipcet@protonmail.com
      Distribution: ---
This is a heads-up about a bug in cygwin/msys2 which may be misreported as a
wine bug.
The Cygwin code assumes CPUID leaf 0x0d to indicate in EBX a 64-byte-aligned
value.  That may or may not be true on current Windows systems, but on current
Linux systems running Wine, with recent CPUs, a CPU feature called "PKU" or
"PKRU" (memory protection keys for userspace), enabled by default, indicates an
additional 8-byte XSAVE area.
This makes the Cygwin code attempt to xsave to a non-64-byte aligned area,
which causes a segfault and abnormal program termination.
While this is clearly a bug, it's a bug that apparently cannot be triggered by
current Windows systems. This means Wine fails to be bug-for-bug compatible in
this case. I don't think there's an easy way around that: we'd have to trap
XGETBV and CPUID instructions to pretend that a feature that is enabled by
Linux actually isn't available.
It would have been nice if the Linux kernel had provided a way to disable the
pku feature on a per-process basis, but AFAICT, it didn't. The nopku kernel
command line argument makes things work, but requires a reboot and disables the
very useful PKU feature for the entire system.
So I don't think there's a good workaround here, but maybe we should suggest to
the Linux kernel people to allow per-process activation of any future XCR0
features?
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[Bug 58420] New: Wine crashes when running msys2 iff CPU's PKU/PKRU feature is enabled