cygwin compiled DLLs

Matthew Brett
Mon Dec 14 04:18:00 GMT 1998

Dear Mumit / fellow DLL sufferers,

Thanks for all your stuff on DLLs on the list, which has been very
helpful.  Sadly, though, I am still stuck trying to link a
Cygwin DLL to a Visual C calling program (and also get a working
matlab mex file from Cygwin, which was my main aim).

I am using b20.1 on NT4 sp3 FAT, and VC++ 4.2.

I think I have tried everything in the dllhelpers 0.2.1 package,
and still get invalid memory references as soon as I try and
access any DLL routine, from a VC binary.  I've attached the
very simple code that I have been using.

Have I made some silly mistake somewhere?
Should I expect this to work yet?

I would be very very grateful for any further thoughts, as I 
am now stuck.

Thanks a lot,

Matthew Brett

For the attached code:
Compile of vcdll, vcmain works fine with:
$ vcmain.c vcdll.c 

and ./vcmain runs without error.
However, trying to compile vcmain.c in VC++ and link to the 
DLL created by with:
> vclink vcmain vcdll
results in in a binary that runs, giving:
"Entering DLL"

followed by the error message:

"The instruction at 0x77f6cc66 referenced memory at 0x00000010"

#! /bin/sh
#, based on Mumit Khan's dllhelper make file.
#  Script to compile relocatable DLL, a calling main program, 
#  and link the relocatable DLL to the calling main program
#  First argument is file for main program (for linking to DLL)
#  Second argument is file for compiling to DLL

# Compile source files:
gcc -c -DBUILDING_DLL=1 -I. -g -Wall  -o ${croot}.o ${croot}.c
gcc -c -DBUILDING_DLL=1 -I. -g -Wall  -o dllinit.o dllinit.c

# Make .def file:
dlltool --export-all --output-def ${croot}.def \
	${croot}.o dllinit.o

# Link DLL.
dllwrap --def ${croot}.def --driver-name gcc -o ${croot}.dll \
    ${croot}.o dllinit.o  

# Build the .a lib to link to:
dlltool --dllname ${croot}.dll --def ${croot}.def \
    --output-lib ${croot}.a

# compile main
gcc -c -I. -g -Wall -o ${main}.o ${main}.c

# link dll function with main
gcc -o ${main}.exe -g -Wall   ${main}.o ${croot}.a
/* vcmain.c */
#include <stdio.h>
int main()
	printf("Entering DLL\n");
	printf("Leaving after DLL\n\n");
/*  vcdll.c  - test DLL function */
#include <stdio.h>
int dll_func()
	printf("Now in DLL\n");
(dllinit.c is dllinit.c from Mumit Khan's dllhelper package)
@echo off
rem vclink.bat
rem BAT file to link GCC dll with VC++ program
rem call with file name roots of main c file, and dll file name
rem e.g vclink main vcdll (where main.c and vcdll.dll are the files required)

set MAINFILE=%1%
set DLLFILE=%2%


rem Compiler parameters
cl -c %MAINFILE%.c

rem Library creation command
echo LIBRARY %DLLFILE%.dll > temp.def
type %DLLFILE%.def >> temp.def
lib /def:temp.def /machine:ix86 /OUT:temp.lib

rem Linker parameters
link %MAINFILE%.obj temp.lib /out:%MAINFILE%.exe
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