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Date:	Fri, 10 Sep 2004 09:56:37 -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: cygwin 1.5.11: execv doesn't set argv[0] on Windows programs
In-Reply-To:	<20040910125048.GB7514@trixie.casa.cgf.cx>
Message-ID:	<Pine.GSO.4.61.0409100946400.12311@slinky.cs.nyu.edu>
References:	<Pine DOT GSO DOT 4 DOT 61 DOT 0409100001520 DOT 2335 AT slinky DOT cs DOT nyu DOT edu> <20040910125048 DOT GB7514 AT trixie DOT casa DOT cgf DOT cx>
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On Fri, 10 Sep 2004, Christopher Faylor wrote:

> On Fri, Sep 10, 2004 at 12:38:31AM -0400, Igor Pechtchanski wrote:
> >Hi,
> >
> >I'm getting the following behavior consistently:
> >[snip]
> >In other words, invoking a Cygwin program sets argv[0] correctly, but
> >invoking a Windows program doesn't.  Interestingly enough, using the MinGW
> >execv works properly:
>
> There is no such thing as "argv[0]" for a Windows program.  Cygwin uses
> CreateProcess to create processes.  CreateProcess does not have the concept
> of "argv[0]".  Perhaps Microsoft's exec functions do something funky that
> is understood by other msvcrt programs.  Cygwin doesn't do that.

Allow me to disagree.  CreateProcess takes two separate arguments: the
image to run, and the command line (yes, as one long line).  The actual
executable being run is the image parameter, but the value of argv[0] is
extracted from the command line one (well, unless the image name is NULL,
in which case the image name and argv[0] are the same).  That's the value
of argv[0] that I meant.

Now, spawn_guts() *seems* to retain the original (correct) argv[0] when
constructing the command line string, but it apparently replaces it with
the prog_arg parameter somewhere for Windows programs...

Hmm, wait a minute, now that I phrased it this way, I think it enabled me
to find the culprit.  Lines 513-515 of spawn.cc say:

      /* Replace argv[0] with the full path to the script if this is the
         first time through the loop. */
      newargv.replace0_maybe (prog_arg);

Is there a particular reason why this is done for ".exe" files?
Thanks,
	Igor
-- 
				http://cs.nyu.edu/~pechtcha/
      |\      _,,,---,,_		pechtcha AT cs DOT nyu DOT edu
ZZZzz /,`.-'`'    -.  ;-;;,_		igor AT watson DOT ibm DOT com
     |,4-  ) )-,_. ,\ (  `'-'		Igor Pechtchanski, Ph.D.
    '---''(_/--'  `-'\_) fL	a.k.a JaguaR-R-R-r-r-r-.-.-.  Meow!

"Happiness lies in being privileged to work hard for long hours in doing
whatever you think is worth doing."  -- Dr. Jubal Harshaw

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