FAST_CWD warning on 64-bit Cygwin + Windows for ARM64
Thu Jan 7 22:15:13 GMT 2021

>Running cygwin64 on Windows for ARM64 using the new, experimental
>x86_64 emulation layer, the following warning is shown:

>> Cygwin WARNING:
>>    Couldn't compute FAST_CWD pointer.  This typically occurs if you're using
>>    an older Cygwin version on a newer Windows.  Please update to the latest
>>    available Cygwin version from  If the problem persists,
>>    please see

>So far, the problem seems to be mostly benign, however was observed by
>a build system which doesn't properly sanitize stderr (the project
>used grep through ant's ExecTask which combines stdout and stderr by

>I don't require help with this issue, but wanted to report it.  As
>Windows on ARM64 becomes more popular, the number of users moving from
>cygwin32 to cygwin64 will increase, and the problem is likely to be
>reported (or at least experienced) more and more.

>I did browse the archives and found this message:

>However it didn't mention Windows ARM64 by name, so I wanted to share,
>I wasn't sure if this is due to a Win32 API change, a bug in x86_64
>emulation for this particular OS or an unforeseen edge-case within the
>cygwin codebase.

>Slightly unrelated, but if a particular project volunteer requires
>ARM64 hardware to reproduce and resolve the above issue, please reply
>to me privately, I'd be happy to help.  Also, thanks for the hard work
>maintaining the project!


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