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Message-ID: <3A048412.F650E99A@ece.gatech.edu>
Date: Sat, 04 Nov 2000 16:48:02 -0500
From: Charles Wilson <cwilson AT ece DOT gatech DOT edu>
MIME-Version: 1.0
To: cygwin AT sources DOT redhat DOT com
Subject: Re: Building C++ DLLs
References: <3A048147 DOT 7005DB68 AT ece DOT gatech DOT edu>
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After spending a half hour writing this message, I just figured it out.
The following procedure works:

c++ -c -DBUILDING_DLL=1 -I. -g  -o dllclass.o dllclass.cc
c++ -c -DBUILDING_DLL=1 -I. -g  -o dllexterns.o dllexterns.cc
c++ -shared -Wl,--export-dynamic -Wl,--output-def=cxxdll.def \
  -Wl,--out-implib=libcxxdll.a -Wl,--enable-auto-image-base \
  -o cxxdll.dll dllclass.o dllexterns.o
Creating library file: libcxxdll.a
c++ -c -I. -g  -o usedll.o usedll.cc
c++ -o usedll.exe -g   usedll.o -L./ -lcxxdll

./usedll works!

The difference was using '-Wl,--export-dynamic' instead of
'-Wl,--export-all-symbols'.  I didn't have to create the def file by
hand or edit it; it "just works" (tm).

--Chuck


Charles Wilson wrote:
> 
> Is it possible to build C++ DLL's using 'c++ -shared' (that is, ld
> --shared) instead of dllwrap?
> 
> I'm running into two problems (experimenting with Mumit's dll-helpers)
> 
> First,
> 
> c++ -c -DBUILDING_DLL=1 -I. -g  -o dllclass.o dllclass.cc
> c++ -c -DBUILDING_DLL=1 -I. -g  -o dllexterns.o dllexterns.cc
> c++ -shared -Wl,--export-all-symbols -Wl,--output-def=cxxdll.def \
>   -Wl,--out-implib=libcxxdll.a -Wl,--enable-auto-image-base \
>   -o cxxdll.dll dllclass.o dllexterns.o
> Cannot export _bss_end__: symbol not defined
> Cannot export _bss_start__: symbol not defined
> Cannot export _data_end__: symbol not defined
> Cannot export _data_start__: symbol not defined
> Creating library file: libcxxdll.a
> collect2: ld returned 1 exit status
> make: *** [cxxdll.dll] Error 1
> 
> Why is ld trying to export "_bss_end__" and friends? Those symbols are
> not referenced anywhere by the source code.
> 
> So, try again.  Take the generated .def file from the previous failure,
> and edit it by hand to remove "_bss_end__" and friends. Second problem:
> 
> c++ -shared \
>   -Wl,--out-implib=libcxxdll.a -Wl,--enable-auto-image-base \
>   -o cxxdll.dll cxxdll.def dllclass.o dllexterns.o
> 
> That works fine! But....try to compile the application that uses the
> dll:
> 
> c++ -c -I. -g  -o usedll.o usedll.cc
> c++ -o usedll.exe -g   usedll.o -L./ -lcxxdll
> /usr/lib/gcc-lib/i686-pc-cygwin/2.95.2-3/libgcc.a(tinfo.o): In function
> `_rtti_class':
> /cygnus/netrel/src/gcc-2.95.2-3/gcc/cp/tinfo.cc(.text+0x60): multiple
> definition of `__rtti_class'
> .//libcxxdll.a(d000064.o)(.text+0x0): first defined here
> collect2: ld returned 1 exit status
> make: *** [usedll.exe] Error 1
> 
> So, I do 'nm -a libcxxdll.a | grep rtti' and get:
> 
> 00000000 I __imp____throw_type_match_rtti
> 00000000 I __imp____rtti_user
> 00000000 I __imp____rtti_si
> 00000000 T ___rtti_ptr
> 00000000 I __imp____rtti_ptr
> 00000000 T ___rtti_ptmf
> 00000000 I __imp____rtti_ptmf
> 00000000 T ___rtti_ptmd
> 00000000 I __imp____rtti_ptmd
> 00000000 T ___rtti_func
> 00000000 I __imp____rtti_func
> 00000000 T ___rtti_class
> 00000000 I __imp____rtti_class
> 00000000 T ___rtti_attr
> 00000000 I __imp____rtti_attr
> 00000000 T ___rtti_array
> 00000000 I __imp____rtti_array
> 
> Note that the importlib generated using the following command:
> 
> dllwrap --implib libcxxdll.a.wrap --driver-name c++ -o cxxdll.dll
> cxxdll.def dllclass.o dllexterns.o
> 
> does not contain any rtti stuff (also, it seems to ignore cxxdll.def and
> generate its own behind the scenes) and allows successfully link/usage
> of the dll.
> 
> 'nm -a libcxxdll.a.wrap | grep rtti' ---> no output
> 
> How can I generate a C++ DLL using c++ -shared (ld --shared) without
> hand-editing a def file, and avoid this rtti garbage...(what is that,
> anyway?)
> 
> Help...
> 
> --Chuck
> 
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