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Date: Wed, 30 Jul 2003 21:01:47 -0700 (PDT)
From: vikramshrowty AT yahoo DOT com
X-X-Sender: vikram AT hidis DOT cjb DOT net
Reply-To: vikramshrowty AT fastmail DOT fm
To: cygwin AT cygwin DOT com
Cc: vikramshrowty AT fastmail DOT fm
Subject: Re: linking with non-cygwin dll
In-Reply-To: <Pine.GSO.4.44.0307302211030.15840-100000@slinky.cs.nyu.edu>
Message-ID: <Pine.LNX.4.50.0307302100420.28744-100000@hidis.cjb.net>
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Perfect. Thanks a lot.


On Wed, 30 Jul 2003, Igor Pechtchanski wrote:

> Vikram,
> 
> Replies inline below.
> 
> On Wed, 30 Jul 2003 vikramshrowty AT yahoo DOT com wrote:
> 
> > You need this for linking with third-party dlls that dont have a
> > cygwin version.
> 
> Yes, you do.  The suggestion of omitting msvcrt.dll is bogus.
> 
> > I was looking through some documentation for the MKS toolkit (it's like
> > a commercial alternative to cygwin) and according to it, a program that
> > uses the MKS c-library can link with dlls that are in turn linked to
> > msvcrt.dll (or whatever provides the msft c library). It seems that as
> > long as you dont try to link in both the c-libraries simultaneously into
> > the same program or dll, it is not a problem.
> 
> Same (or similar enough) with Cygwin.
> 
> > So, for code in the dll, stdout refers to msft::stdout whereas in the
> > main program, it refers to cygwin::stdout. I was wondering if this is
> > an issue of gcc not setting things up to properly call the dll's entry
> > and exit functions or something like that. When you are linking the
> > main program you do ...
> >
> > > gcc -Wall  -g -o test.exe test.c -L. -lgcc -ldll
> >
> > Note the absence of the -mno-cygwin, because your main program is a
> > cygwin program.
> 
> Correct.
> 
> > Could this mean that the non-cygwin dll's entry and exit points are not
> > setup to be called automatically?
> 
> No, they should be called properly.
> 
> However, note that the two runtimes are sharing the output stream (tty,
> file descriptor, what have you), but aren't sharing the stdio data
> structures.  Also, since the main program is linked as a Cygwin program,
> msvcrt's exit() function is *not* called (the Cygwin gcc library one is
> called instead).  Thus, the gcc library exit() flushes the buffers of the
> gcc library's stdio implementation, and the msvcrt stdio buffers remain
> unflushed.
> 
> Does the above explain things adequately?
> 	Igor
> 
> > On Wed, 30 Jul 2003, Martin Gainty wrote:
> >
> > > I would go so far as to suggest taking MSVCRT.dll off the path altogether
> > > After all why have 2 runtimes?
> > > -Martin
> > > ----- Original Message -----
> > > From: "Igor Pechtchanski" <pechtcha AT cs DOT nyu DOT edu>
> > > To: <vikramshrowty AT fastmail DOT fm>
> > > Cc: <cygwin AT cygwin DOT com>
> > > Sent: Wednesday, July 30, 2003 6:03 PM
> > > Subject: Re: linking with non-cygwin dll
> > >
> > > > On Wed, 30 Jul 2003 vikramshrowty AT yahoo DOT com wrote:
> > > >
> > > > > Hi,
> > > > >         I had posted a query earlier about a cygwin program linking
> > > > > with a non-cygwin dll. Based on the very helpful responses and some
> > > > > googling around, I learnt that this is possible. But...
> > > > >
> > > > > heres a main.c that links with cygwin1.dll
> > > > >
> > > > > int main(void)
> > > > > {
> > > > >   printf("CYGWIN\n");
> > > > >   test_dll();
> > > > >   return(0);
> > > > > }
> > > > >
> > > > > where test_dll is in a dll compiled with -mno-cygwin and is defined
> > > > > like this...
> > > > >
> > > > > __declspec(dllexport) __stdcall void test_dll(void)
> > > > > {
> > > > >   printf("MSFT %d\n",i);
> > > > >   fflush(stdout);
> > > > > }
> > > > >
> > > > > This works perfectly. But, notice the fflush. If this is removed,
> > > > > "MSFT" doesnt get printf'ed. I assuming that this is because the
> > > > > stdout buffer in the microsoft c-library isnt getting flushed
> > > > > automatically at program exit.
> > > > >
> > > > > Any ideas on why?? ..and how to remedy this??
> > > > > --Vikram
> > > >
> > > > Well, gcc links the Cygwin executable with its own C runtime.  MSVCRT is
> > > > another C runtime.  So, when you call the DLL, you have 2 C runtimes
> > > > competing for the same output stream.  This can't be good (in fact, the
> > > > results are unspecified, IIRC).  Thus, the simple remedy is: don't do
> > > > that.  Either only use one runtime for output (whichever one), or fflush
> > > > and pray.
> > > > Igor
> 
> 

-- 
--Vikram

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