From: fjh AT cs DOT mu DOT OZ DOT AU (Fergus Henderson)
Subject: Re: DLL Problem
25 Aug 1997 16:48:47 -0700
Approved: cygnus DOT gnu-win32 AT cygnus DOT com
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Message-ID: <199708250613.QAA27153.cygnus.gnu-win32@murlibobo.cs.mu.OZ.AU>
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Original-To: geier AT forwiss DOT uni-passau DOT de (Roland Geier)
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In-Reply-To: <199708212048.WAA07599@bombadill.forwiss.uni-passau.de> from Roland Geier at "Aug 21, 97 10:48:23 pm"
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Roland Geier wrote:
> [someone wrote:]
> > I'm trying to port a tcl module from unix to win95 as a dll to load within
> > wish.
....
> > ext+0x15):libcmain.cc: undefined reference to `GetCommandLineA AT 0'
> > c:/gnuwin32/b18/H-i386-cygwin32/i386-cygwin32/lib/libcygwin.a(libcmain.o)(.t
> >
> > ext+0x1e):libcmain.cc: undefined reference to `WinMain AT 16'
> >
> > This seems to be a reentrancy problem, since a simple call like :
> > fprintf(stderr, ...)
> 
> ...for me this seems to be a forgotten '-lkernel32' at link-time :). The
> undefined ref to 'WinMain' can be avoided with:
> 
>         echo 'int main() { return 0; }' > fixup.c;
>         echo 'asm (".section .idata$3\n" ".long 0,0,0,0,0,0,0,0");' >> fixup.c;
>         gcc -c fixup.c
>         # link fixup.o with your dll...

Defining main() will supress the link error, but it will not actually
fix the problem.  The startup file (crt0.o, I think) containing a
definition of `_impure_ptr' will be linked in, but _impure_ptr will
not be initialized.  This means that any reference to global variables
such as `stdout' or `stderr' from within your DLL will be broken, and
so your DLL will probably crash.

To avoid the problem, you need to initialize your DLL's _impure_ptr
from the main program.  See <http://www.cs.mu.oz.au/~fjh/gnu-win32>
for an example of how to do this.

-- 
Fergus Henderson <fjh AT cs DOT mu DOT oz DOT au>   |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>   |  of excellence is a lethal habit"
PGP: finger fjh AT 128 DOT 250 DOT 37 DOT 3         |     -- the last words of T. S. Garp.
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