fork issue when lauching cygwin64 process from 32bit native app on Windows 10 TH2

David Macek
Tue Dec 1 21:44:00 GMT 2015

On 1. 12. 2015 18:40, David Macek wrote:
> On 1. 12. 2015 15:01, Corinna Vinschen wrote:
>> On Dec  1 21:07, nu774 wrote:
>>>> There must be a bug in the new CMD somewhere.  But, anyway, I'll look
>>>> into it when I finally managed to update my W10 test machine.
>>> No, cmd.exe is just an example. Any 32bit process can be an trigger.
>>> I guess something has changed in TH2 kernel regarding process memory
>>> management or something that interferes cygwin's fork().
>> If that only happens w/ 64 bit Cygwin started from a 32 bit parent, then
>> there's some foul-up in the WOW64 layer in terms of starting 64 bit
>> processes, perhaps.  Sigh, it's a rather unexpected change after it
>> worked fine for so long :(
> Yup. I can confirm.

Just for the record, we did some debugging over IRC and it seems it's an issue with WOW64 where the stack in the first 64-bit process is offset for some reason.

Citing Corinna: "I wonder if we have to resurrect the old wow64_respawn_process function for this border case"

David Macek

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