To: cygwin AT cygwin DOT com
From: Thorsten Kampe <thorsten AT thorstenkampe DOT de>
Subject:  Re: Using a Cygwin-built DLL outside of Cygwin
Date:  Wed, 17 Oct 2007 23:53:57 +0100
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References:  <1192647409 DOT 21421 DOT 528 DOT camel AT strangepork>
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* Christian Kreibich (Wed, 17 Oct 2007 11:56:49 -0700)
> I have a library originally developed on Linux/FreeBSD that is building
> fine on Cygwin. It also works fine if I build executables using this
> library inside Cygwin. The goal however is for the resulting DLL to work
> outside of Cygwin, for example with Visual Studio. I am running into a
> few problems trying to achieve this. I'll first describe what I've
> tried, and ask questions below.
> 
> Following http://www.cygwin.com/ml/cygwin/2004-03/msg00453.html , I use
> this command to link the library:
> 
> gcc -shared  ${objects} \
> 	-Wl,--output-def=.libs/cygfoo.def \
> 	-Wl,--export-all-symbols \
> 	-Wl,--enable-auto-import \
> 	-Wl,--enable-auto-image-base \
> 	-Wl,--add-stdcall-alias \
> 	-Wl,--enable-stdcall-fixup \
> 	-Wl,--enable-auto-image-base \
> 	-o .libs/cygfoo-0.dll \
> 	-lssl -lcrypto
> 
> (The library uses OpenSSL, which I have included in my Cygwin setup.)
> 
> I threw out --compat-implib since it no longer seems to exist (per "man
> ld"). I originally also used --out-implib to generate an import library,
> but like http://www.cygwin.com/ml/cygwin/2000-10/msg01051.html I'd get a
> 'multiple ".text" sections found with different attributes' warning when
> using the resulting implib. (I have also tried the command shown at
> http://cygwin.com/cygwin-ug-net/dll.html , with the same result.)
> 
> I now instead use MSVC's lib command, which seems to fix that problem:
> 
>   LIB /machine:ix86 /def:cygfoo.def /out:cygfoo.lib
> 
> Given the resulting .dll, .lib, and .def, I can compile a dummy
> application in MSVC. However, this executable has two problems. First,
> output to stdout/stderr does not appear. A number of people seem to have
> noticed this. One related posting recommended the use file I/O instead,
> but if I attempt this (or indeed any cross-DLL-boundary calls), the
> application crashes. Simpler function calls whose execution paths don't
> leave my DLL work fine.
> 
> My questions:
> 
> - Is there a Cygwin-only way to avoid the MSVC lib command detour, to
> avoid the "multiple .text sections" issue?
> 
> - I have gleaned from related postings and FAQ 6.12 that the crashes are
> due to the use of cygwin1.dll and msvcrt.dll (and/or related Windows
> DLLs) in the same executable. Is this correct?
> 
> - If so, is there a way to avoid the problem while still building the
> library in my cozy Cygwin/POSIX environment? My understanding is that
> -mno-cygwin doesn't help in that regard (per FAQ 6.10), and that I have
> to keep cygwin1.dll (per FAQ 6.11).
> 
> - If getting rid of msvcrt.dll is the answer, what are the implications
> for building Windows-native applications? (And, assuming this is
> possible, if a kind soul could tell me how I'd go about doing this even
> though it's not a question at the heart of this list, that'd be much
> appreciated...)

Aren't these FAQs?

* Can I link with both MSVCRT*.DLL and cygwin1.dll?
http://cygwin.com/faq/faq.programming.html#faq.programming.msvcrt-and-
cygwin

* How do I use cygwin1.dll with Visual Studio or MinGW?
http://cygwin.com/faq/faq.programming.html#faq.programming.msvs-mingw


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