RE: Cygwin x86 on Windows 10 ARM64

[David Allsopp <David dot Allsopp at cl dot cam dot ac dot uk>]

Corinna Vinschen wrote:
> On Jul 12 07:46, David Allsopp wrote:
> > Corinna Vinschen wrote:
> > > On Jul 10 10:51, 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/base-files-mketc.sh to exit with an error all the
> > > > time. I wonder if there's a possible workaround to make
> > > that less intrusive?
> > >
> > > Try if C:\Windows\Sysnative\drivers\etc works.  That should be the
> > > easiest way to fix the issue in the script.
> >
> > It does indeed. Certainly seems like a good fallback (if not possible
> > default, although I'm sure someone out there takes advantage of a
> > different hosts file between 32-bit and 64-bit!!). I'm happy to tweak
> > the script if you can remind me where its repo is?
> 
> https://sourceware.org/cygwin-apps/ has a list of Cygwin-specific projects
> hosted on cygwin.com.  The base-files project is maintained by Achim
> Gratz.  Please send patches to the cygwin-apps mailing list.

Thanks - will do!

> > > > 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.
> > > >
> > > > The other is that all Cygwin binaries are emitting the "Could not
> > > > compute FAST_CWD pointer" warning.
> > >
> > > Nothing we can do about, unless somebody dives into assembler code
> > > on such a system.  If the code switches to ARM64 early, this could
> > > be tricky.
> >
> > The machine I'm using is only for testing on this platform - I can
> > grant access to it if it'd be worth looking into?
> >
> > > As a workaround I pushed a patch to check for running in WOW64 under
> > > ARM64.  The warning is skipped then.  The already existing fallback
> > > code should work most of the time.  Just give the latest developer
> > > snapshot from https://cygwin.com/snapshots/ a try.
> >
> > OK, so this is very weird - both GetNativeSystemInfo and GetSystemInfo
> > are returning 0 in both wProcessorArchitecture and wReserved (and FWIW
> > 586 in dwProcessorType). This is with GCC 6.4.0 (i686-w64-mingw32-gcc)
> > and with Microsoft's own **x86** Cl (19.15.26629.1 in VS 2017.8
> > Preview 4). My test program is simply:
> 
> This looks like a bug in the emulator.  You may want to contact Microsoft.

Indeed - I can't install the fast ring insider build on this machine (driver problem <sigh>) but I'm now trying the slow ring instead.

> Nevertheless, we can use the current buggy reply to our advantage:
> We know we're running in an emulator.  The value of wProcessorArchitecture
> returned by GetNativeSystemInfo should never be 0.  6, 9, 12 are ok, but
> 0???

Seems reasonable!

> So, if the GetNativeSystemInfo returns 0 we can still skip the warning.
> For completeness, I'd like to see the output of `uname -a'
> in Cygwin, though.

CYGWIN_NT-10.0-WOW Envy 2.11.0(0.327/5/3)  i686 Cygwin


David

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