troubles w/ dll building and crtdll-vs-msvcrt

Mumit Khan khan@xraylith.wisc.EDU
Mon May 31 21:10:00 GMT 1999

Paul Thiessen <> writes:
> Yes, sorry to be a broken record... another post about this - I'm still
> getting page faults when loading in a dll I've built myself, and am trying
> to track down the problem.

btw, I do appreciate your reports, even if you do sound like a broken
record ;-).

>   I'm using mingw32/egcs. For an example, take Mumit's "dllhelper" sample
> dll build for c++. Using the provided makefile, "make" gives the following 
> output:
> c++ -c -DBUILDING_DLL=1 -I. -g  -o dllclass.o
> c++ -c -DBUILDING_DLL=1 -I. -g  -o dllexterns.o
> gcc -c -DBUILDING_DLL=1 -I. -g  -o dllinit.o dllinit.c
> dllwrap --export-all --output-def cxxdll.def --implib libcxxdll.a\
> 	--driver-name c++ -o cxxdll.dll \
>     dllclass.o dllexterns.o dllinit.o
> Warning: no export definition file provided
> dllwrap will create one, but may not be what you want
> c++ -c -I. -g  -o usedll.o
> c++ -o usedll.exe -g   usedll.o -L./ -lcxxdll
> When I run the program, usedll.exe gives correct output. However, when I
> try to run it in gdb, I get a segmentation fault:
> c++> gdb usedll
> GNU gdb 4.17.1 (... + welcome message)
> (gdb) run
> run
Starting program: D:\dllhelpers-0.2.5\c++/usedll.exe
> 67480000:D:\DLLHELPERS-0.2.5\C++\CXXDLL.DLL
> Program received signal SIGSEGV, Segmentation fault.
> 0x78008484 in <bad string table offset> ()
> (gdb)
> Then, when I follow Mumit's advice about how to prevent linking with
> crtdll.dll, and do the final program linking with gcc instead of c++, it
> goes through okay:

Just after I sent the last note saying there shouldn't be any problems
with the current scheme, I found out I was wrong! Programs keep on dying
die under gdb, and till your report, I had no idea why. Thanks.

At the risk of sounding like a broken record, it is fixed for egcs-1.2.

For those using msvcrt runtime add-on, I'll upload new drivers (g++/c++
and g77) sometime next week so you won't need the workaround anymore.

> I'm not sure what all this means - whether the problem is with gdb or
> something more subtle. But I have a more complicated dll (made out of the
> togl opengl-to-tcl-widget program) that I'm trying to link into a program
> with the same dll building technique. If I just use the togl.o file linked
> statically, all is fine, but once I try to use the togl.dll I built, I
> just get page faults (win95 claims in msvcrt.dll) at runtime, no matter
> how I do the program linking. crtdll.dll is still being linked in,
> possibly because other libraries I need depend on it.
>   I don't know exactly what I'm asking - I guess I still don't fully
> understand the dll building process, and perhaps all this is fixed in egcs
> 1.2... Oh well.

If you specify '-v' when linking (either via gcc/c++/g77 or dllwrap),
you'll see if -lcrtdll is being specified or not. You'll see that g++
and g77 do this no matter what since it's compiled in.


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