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Date: Mon, 22 Sep 2025 14:23:10 +0200
Message-ID: <CAPJSo4VsfhmURL3qoXcu9_dcw6pAZQHq9bpiybPSO=v4w-Cxqg@mail.gmail.com>
Subject: Re: Why does Cygwin not use MiCloneProcessAddressSpace() for fork()
To: "cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Content-Type: multipart/mixed; boundary="0000000000002aac74063f62e4ce"
From: Lionel Cons via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Lionel Cons <lionelcons1972 AT gmail DOT com>
Sender: "Cygwin" <cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com>

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On Mon, 22 Sept 2025 at 13:55, Lionel Cons <lionelcons1972 AT gmail DOT com> wrote=
:
>
> 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 r=
esults
> > > 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 =E2=80=93 something we inevitably nee=
d 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 th=
reads 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.

Attached is a proof that threads (in child and parent process) and
RtlCloneUserProcess() work together:
winforktest1.c.txt

Lionel

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