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Date: Mon, 22 Sep 2025 13:55:14 +0200
Message-ID: <CAPJSo4VbBtzTKqyy+oT0qp9QEUyGktxWyZtDPY1D89_cE4ximg@mail.gmail.com>
Subject: Re: Why does Cygwin not use MiCloneProcessAddressSpace() for fork()
To: "cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
From: Lionel Cons via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Lionel Cons <lionelcons1972 AT gmail DOT com>
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On Mon, 22 Sept 2025 at 13:28, Old, Oliver via Cygwin <cygwin AT cygwin DOT com> wrote:
>
> Mark Liam Brown wrote:
> > This is exposed to the userspace as NtCreateProcessEx() as documented in
> > https://github.com/huntandhackett/process-cloning
>
> From the linked page:
> > Unfortunately, it doesn't matter which method we prefer because the results
> > will be identically disappointing: STATUS_PROCESS_IS_TERMINATING, or, in other
> > words, "An attempt was made to access an exiting process." The system
> > considers the cloned threadless process as waiting for deletion and, thus,
> > refuses to create threads in it – something we inevitably need to execute
> > code. Sorry, but NtCreateProcessEx-based cloning is incompatible with code
> > execution.
> >
> > > Note that it wasn't always the case. The kernel allowed creating threads in
> > > such processes until Windows 8.1.

That was a bug, long fixed. UWIN added pthread support at some point,
so yes, threads and RtlCloneUserProcess() do work together.

Lionel

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