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X-Authentication-Warning: slinky.cs.nyu.edu: pechtcha owned process doing -bs
Date: Thu, 8 Jul 2004 11:23:41 -0400 (EDT)
From: Igor Pechtchanski <pechtcha AT cs DOT nyu DOT edu>
Reply-To: cygwin AT cygwin DOT com
To: cygwin AT cygwin DOT com
Subject: Re: negative error status: gcc vs. cl
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On Thu, 8 Jul 2004, Christopher Faylor wrote:

> On Thu, Jul 08, 2004 at 10:25:09AM -0400, Igor Pechtchanski wrote:
> >On Thu, 8 Jul 2004, Corinna Vinschen wrote:
> >
> >> On Jul  8 11:49, Daniel Lungu wrote:
> >> > Feel like bash tcsh on Cygwin mess up with negative exit status
> >> > from a cl compiled .exe
              ^^^^^^^^^^^^^^^^
> >> The answer is "don't do that".  Use positive values in the range from
> >> 0 to 255.  See
> >> http://www.opengroup.org/onlinepubs/009695399/functions/exit.html
> >
> >Actually, it looks like another buglet in Cygwin.  The code in
> >spawn_guts() in spawn.cc (line 847 in CVS HEAD) simply binary-ORs the
> >exitcode value returned by GetExitCodeProcess with the "res" variable.
> >However, the "res" variable is also used to carry some flags, and a
> >negative exitcode, being a full DWORD, accidentally sets those, so all
> >sorts of havoc can potentially occur (and I'm surprised that all that
> >happens is the wrong exit code).
>
> This is not a bug.  A cygwin program can't set a negative exit code.
> Only the lower order 16 bits are used.  This is enforced by _exit.
>
> If someone uses ExitProcess in a cygwin program, then well, err...
> cgf

You would be right if spawn() could only be used for Cygwin programs.
Unfortunately, it can also be used for non-Cygwin programs (as shown by
the underlined phrase above) which don't operate under the above
restriction.  So, I'd say that binary-ANDing the exitcode value with 0xFF
(or 0xFFFF if you want 16 bits) is a healthy precaution.  It will
certainly do no harm, and it will make absolutely sure that the other
flags (e.g., EXIT_REPARENTING) are never tread upon.
	Igor
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