Re: Building GNUstep for Windows using Clang

[David Chisnall]

On 05/03/2020 00:43, Frederik Seiffert wrote:
> Thanks David. I made some progress with this setup, although it does 
> feel like we’re a bit off the beaten track here (again)...
>
> To get libobjc linking with the MinGW clang toolchain using LLD I had to 
> create an import library (.dll.a) as outlined on the MinGW website:
> http://www.mingw.org/wiki/CreateImportLibraries
>
> Basically I ran "dumpbin /exports objc.dll" to get the list of symbols, 
> used that to manually create a objc.def file, and then ran "dlltool -d 
> objc.def -l objc.dll.a". One thing I noticed is that this doesn’t seem 
> to include global variables (e.g. _objc_unexpected_exception), so these 
> won’t be picked up by GNUstep configure and thus native exception 
> support won’t work.
>
> In the end however I switched to using the llvm-mingw toolchain 
> (https://github.com/mstorsjo/llvm-mingw), which defaults to LLD and 
> directly picks up the objc.lib without the need for the import library 
> (but also doesn’t seem allow linking global variables).
>
> I also had to remove "OBJ_MERGE_CMD_FLAG" in config.make, as LLD doesn’t 
> support the -r flag for incremental linking.

Hmm, that probably means that -base Additions won't build.

> With this and a couple more configure flags I got Base to start 
> compiling, but I’m now stuck at the Additions subproject failing to link 
> because it seems to be missing all the necessary linker flags:
>
> > clang -nostdlib        -o ./obj/subproject.o 
> > obj/Additions.obj/GSTypeEncoding.c.o ...
> > lld-link: error: <root>: undefined symbol: _mainCRTStartup
> > lld-link: error: undefined symbol: _malloc
> > lld-link: error: undefined symbol: __declspec(dllimport) _object_getClass
> > ...
>
> Does anyone with better knowledge of GNUstep make have an idea of why 
> this might happen or how to debug this further?

If you're not using -r, then I don't know what this .o will be.  The 
subproject thing is a source of constant pain because almost nothing 
other than GNUstep uses -r, so it tends to be horribly buggy.  It's 
supposed to take a load of .o files and generate a .o file that can be 
linked as if it were the original list of .o files.  Modern build 
systems just pass the list of .o files around.

> > There is a bug somewhere in the SEH support that I need to look for. 
> >  I suspect it is in clang - EH seems to fail with ARC and I think that 
> > it may be to do with the ARC calls not being correctly emitted in the 
> > funclet.  Dustin is planning on looking at some of the Clang funclet 
> > issues.
>
> That’s good to know, thanks.
>
> By the way, is libcxxrt needed on Windows for ObjC++ EH on Windows? 
> Seems like WinObjC is not using it.


No, libcxxrt implements the Itanium C++ ABI.  On Windows, libobjc2 
supports the Visual Studio C++ ABI, so exceptions should interop with 
C++ libraries compiled with clang or MSVC.

David