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Subject:	Re: Aren't Windows System Error popups meant to be disabled in Cygwin?
To:	cygwin AT cygwin DOT com
Cc:	Brian Inglis <Brian DOT Inglis AT systematicsw DOT ab DOT ca>
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From:	David Allsopp via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	David Allsopp <david AT tarides DOT com>
Sender:	"Cygwin" <cygwin-bounces+archive-cygwin=delorie DOT com AT cygwin DOT com>

On Wed, 31 Jan 2024 at 22:27, Brian Inglis via Cygwin <cygwin AT cygwin DOT com> wrote:
>
> On 2024-01-31 06:40, David Allsopp via Cygwin wrote:
> > Starting with this very trivial C program:
> >
> > #include <stdio.h>
> > #include <zstd.h>
> >
> > int main(void) {
> >    printf("Zstandard v%d\n", ZSTD_versionNumber());
> > }
> >
> > and compiling with
> >
> > x86_64-w64-mingw32-gcc -o test.exe test.c -lzstd
> >
> > when I then run ./test.exe, I get the Windows critical-error-handler
> > dialog stating "The code execution cannot proceed because
> > libzstd-1.dll was not found. Reinstalling the program may fix this
> > problem."
> >
> > My question is not how to fix the problem (I'm well aware of that),
> > but rather why that message is being displayed at all, and is it a bug
> > in Cygwin somewhere? All I could find Googling was previous
> > suggestions that Cygwin routinely calls SetErrorMode with, amongst
> > other things, SEM_FAILCRITICALERRORS with the intention of suppressing
> > this dialog.
> >
> > Is that correct, and if so is this just me? :o)
> >
> > Windows 10 22H2, Cygwin 3.4.10, running all the commands from mintty.
> > I also get the same popup if I run C:\cygwin64\bin\sh -c
> > "/cygdrive/c/path/to/test" either from a Command Prompt or even from
> > "Start -> Run". Running this via "sh" called from a non-Cygwin process
> > (itself invoked from a Command Prompt) which has also called
> > SetErrorMode is how I hit this.
>
> Better to let you know that there is a problem, and what the problem is, so you
> can fix it!

Thank you, but no - as I made clear by:

> My question is not how to fix the problem (I'm well aware of that)

I'm fully aware what has caused the issue to arise, and how to fix it
- that's not the issue. The problem is that according to previous
messages, and the Cygwin code, my impression was that mintty / bash /
sh (*Cygwin* programs) calling this executable should be returning an
exit code here, not freezing on a message dialog. The problem appears
to be a bug in the Cygwin DLL, and from previous messages on the list,
my question is whether it's a regression, and can be fixed.

The reason it's a problem is, say, a script _in Cygwin_ which is
handed a command to run, runs it, and is then completely blocked by
that popup dialog. It's the responsibility of the _caller_ (a Cygwin
program) to indicate the mode in which a program is executed - the
message box may be owned by the program called, but it's caused by it
being loaded, before it has a chance to run any code.

My understanding, based on this line:

https://github.com/cygwin/cygwin/blob/main/winsup/cygwin/dcrt0.cc#L721
in dll_crt0_0

is that Cygwin executables (in this case mintty / bash / sh, etc.)
should be running with SEM_FAILCRITICALERRORS enabled, following the
best practice recommendations in
https://learn.microsoft.com/en-us/windows/win32/api/errhandlingapi/nf-errhandlingapi-seterrormode
and that that setting should be correctly inherited by processes they
call (including non-Cygwin ones).

Some ancient history, reporting my same issue in 2004:
https://cygwin.com/pipermail/cygwin/2004-March/115553.html and this
thread from 2006
https://cygwin.com/pipermail/cygwin/2006-August/150038.html strongly
indicating that that line dcrt0.cc is there precisely to stop this
popup.

Thanks,


David

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