Re: Building GNUstep for Windows using Clang

[Frederik Seiffert]

Hi David,

> Am 20.01.2021 um 18:15 schrieb David Chisnall <gnustep@theravensnest.org>:
> 
> For reference, the $_OBJC_CLASS symbols are meant to be exported from a DLL, 
> they are the canonical pointers to the classes.  The $_OBJC_REF_CLASS 
> pointers are private to a library and are the pointer that code should use 
> for references to a given class.  These are initialised to the corresponding 
> $_OBJC_CLASS variables and the runtime can update them to something different 
> if we change the structure of the class structure in a future ABI.

Thanks for the clarification, that’s helpful. I tried defining the symbols as 
"constant" in the module definition file, and that somehow fixed the linker 
error:

        EXPORTS
            $_OBJC_CLASS_Test CONSTANT
            $_OBJC_REF_CLASS_Test CONSTANT

This was totally by chance, but if I understand it correctly this means an 
undecorated version (without "_imp_" prefix) is emitted to the import library:
https://docs.microsoft.com/en-us/cpp/build/importing-using-def-files?view=msvc-160


There’s one more issue though: both [Test class] and [Test new] (with "Test" 
being defined in the DLL) only return null pointers in my testing. However 
subclassing the Test root class locally works fine and allows instantiating the 
subclass, as does a locally defined root class (same implementation as Test).

The following code (with "Sub" being a subclass of "Test"):

        printf("%p %p\n", [Test class], [Test new]);
        printf("%p %p\n", [Sub class], [Sub new]);

Prints:

        0000000000000000 0000000000000000
        00007FF73EDB0080 00000291D99247A8


Any idea? All other things I tried so far seemed to be working fine, though I’m 
sure this won’t be the last of my questions...

Frederik