Cygwin x86 on Windows 10 ARM64

David Allsopp
Tue Jul 10 20:25:00 GMT 2018

Brian Inglis wrote:
> On 2018-07-10 03:51, David Allsopp wrote:
> > I've been trying out the x86 emulation in Microsoft's ARM64 version of
> > Windows 10 1803.
> >
> > I had two issues with Cygwin x86. The first, which is simple, is that
> > Windows doesn't by default create C:\Windows\SysWOW64\drivers\etc
> > which causes /etc/postinstall/ to exit with an
> > error all the time. I wonder if there's a possible workaround to make
> that less intrusive?
> > The error message implies that it may have computed the wrong
> > directory, which it hasn't - it's just that the directory doesn't exist.
> Do C:\Windows\{System32,SysNative,Sys*}\drivers\etc exist under the
> emulator?
> What does "cygpath -SU" show?

cygpath -SU gives /proc/cygdrive/c/Windows/SysWOW64

Checking within C:\Windows\SysWOW64\cmd.exe (i.e. x86 cmd):

C:\Windows\System32\drivers\etc exists and contains expected files
C:\Windows\Sysnative\drivers\etc exists and contains expected files (looks identical to System32, as you'd hope)
C:\Windows\SysArm32\drivers does not contain an etc directory (but wasn't referenced)
C:\Windows\SysWOW64\drivers didn't contain an etc directory (I created one to silence the error)

So perhaps on WOW64 it would be worth falling back to Sysnative if etc isn't found? Or even just using Sysnative by default in WOW64?

> > The other is that all Cygwin binaries are emitting the "Could not
> > compute FAST_CWD pointer" warning.
> It is just a warning and everything should run normally: what would
> normally be an ntdll entry point on x86 is probably a thunk or trampoline
> to
> arm64(ISA)/aarch64(mode)/armv8(design) code.

Does it potentially make anything slower? (being slightly lazy - I could look at the code and see precisely what it's for).


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