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Date: Mon, 10 Apr 2006 09:48:10 -0400 (EDT)
From: Igor Peshansky <pechtcha AT cs DOT nyu DOT edu>
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To: cygwin AT cygwin DOT com
Subject: Re: Cygwin backwards compatibility break with WinMain and GetCommandLine  (was Re: WinMain() not getting cl...)
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On Sun, 9 Apr 2006, Christopher Faylor wrote:

> On Tue, Apr 04, 2006 at 11:44:47AM -0700, David Rothenberger wrote:
> >WinMain() in a program compiled with cygwin1.dll is no longer
> >getting passed the command-line from bash correctly with the
> >20060403 snapshot. It works fine with the 20060329 snapshot.
> >
> >This is the same problem mentioned in
> ><http://cygwin.com/ml/cygwin/2005-09/msg00298.html>.
> >
> >The same test case is attached here again (winCmdLine.c). I compile
> >it with "gcc -o winCmdLine winCmdLine.c" (note no -mno-cygwin).
>
> This is due to recent changes which cause cygwin to stop filling out the
> command-line for cygwin1.dll using programs.  We did this to fix the
> "long command line" problem.
>
> There is a crude workaround for the problem which reinstates the
> previous cygwin behavior but I really would rather not go that way.  It
> would be nice if, just this once, we could make cygwin a little faster
> at the expense of programs which are using a non-linux-like interface.
>
> So, I'm thinking that if you want your WinMain or GetCommandLine using
> program to work with Cygwin 1.5.20 then you'll have to relink it.  I
> realize that this is a major departure from previous stated goal of
> maintaining backwards compatibility but we've already broken that once
> in recent memory with the case of pure Windows environment variables so
> I think we probably will just take the logical next step and break
> things for WinMain and GetCommandLine as well.
>
> If there are a lot of programs out there which are using WinMain or
> GetCommandLine then I guess we'll hear about it.  Otherwise, unless
> someone can convince me that this is a bad idea, Cygwin will start
> carrying a GetCommandLine substitute which regenerates the command line
> from the argv list.  I have something ready to go in my sandbox now
> but I thought I'd hold off doing this in case someone had a valid
> objection to this approach.

One argument against doing this is that people will now have to build and
distribute 2 versions of each such program -- one that works on 1.5.20,
and one that works on all previous versions of Cygwin.  However, I think
there *is* a way of writing the program so that it will work on both
versions, by using something like the following (untested) function:

typedef LPTSTR WINAPI (*GCL_PTR)(void);
LPTSTR WINAPI cygwinGetCommandLine(void) {
   HMODULE cygDLL, winDLL;
   GCL_PTR cygGCL, winGCL;
   cygDLL = GetModuleHandle(TEXT("cygwin1.dll"));
   cygGCL = (GCL_PTR) GetProcAddress(cygDLL, TEXT("GetCommandLine"));
   if (cygGCL != NULL) return cygGCL();
   winDLL = GetModuleHandle(TEXT("kernel32.dll"));
   winGCL = (GCL_PTR) GetProcAddress(winDLL, TEXT("GetCommandLine"));
   if (winGCL != NULL) return winGCL();
   return NULL;
}

and prefacing the rest of the program by:

#define GetCommandLine cygwinGetCommandLine

Barring some typos in the above, it should work.
WinMain would be a bit harder to emulate, but still possible using the
same techniques as above.

David, could you try this with your testcase and see if my claim is
correct?
	Igor
-- 
				http://cs.nyu.edu/~pechtcha/
      |\      _,,,---,,_	    pechtcha AT cs DOT nyu DOT edu | igor AT watson DOT ibm DOT com
ZZZzz /,`.-'`'    -.  ;-;;,_		Igor Peshansky, Ph.D. (name changed!)
     |,4-  ) )-,_. ,\ (  `'-'		old name: Igor Pechtchanski
    '---''(_/--'  `-'\_) fL	a.k.a JaguaR-R-R-r-r-r-.-.-.  Meow!

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that!" -- Rostand, "Cyrano de Bergerac"

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