fix warning on wingui/pdcscrn.c MSYS2 ARM64

[nhmall]

compiling on MSYS2 Windows 11 ARM64

clang version 21.1.5
Target: aarch64-w64-windows-gnu
Thread model: posix
InstalledDir: C:/msys64/clangarm64/bin

../wingui/pdcscrn.c:1622:16: warning: unknown attribute 'force_align_arg_pointer' ignored
[-Wunknown-attributes]
1622 | static LRESULT ALIGN_STACK CALLBACK WndProc (const HWND hwnd,
| ^~~~~~~~~~~
../wingui/pdcscrn.c:1617:36: note: expanded from macro 'ALIGN_STACK'
1617 | #define ALIGN_STACK attribute((force_align_arg_pointer))
| ^~~~~~~~~~~~~~~~~~~~~~~
1 warning generated.

[Bill-Gray]

Because force_align_arg_pointer only makes sense on x86, I was going to say that the test really ought to be "is this an x86 build" (rather than "is this anything but 64-bit ARM"). That would give us

#if defined(_WIN32) && defined(__GNUC__) 
#   if( defined( _M_IX86) || defined( __x86_64__)
#      define ALIGN_STACK __attribute__((force_align_arg_pointer))    
#   endif
#endif

(Or something similar; I didn't actually test the above and am not sure it gets all x86 systems.)

However, I then wondered if there might be a way just to check to see if force_align_arg_pointer exists, and there is. With that, we have

#if defined( __has_attribute)
#   if __has_attribute( force_align_arg_pointer)
#      define ALIGN_STACK __attribute__((force_align_arg_pointer))
#   endif
#endif

This Works On My Machine™ (which is x86-based), and seems like a more general solution. Does it work on yours? (I need to get a Raspberry Pi or similar for testing such things...)

Thanks for pointing this out.

[Bill-Gray]

Sorry, I should have mentioned : the above will set ALIGN_STACK if the attribute isn't available. If it isn't (as on your ARM64 system), we need to follow that with

#if !defined( ALIGN_STACK)
   #define ALIGN_STACK
#endif

[nhmall]

The pull request was updated to reflect the suggestion from @Bill-Gray. His suggested alternative tested correctly on two platforms.

It defined ALIGN_STACK to nothing on ARM64 as intended, and continued to define ALIGN_STACK to attribute((force_align_arg_pointer)) on an x64 platform.

[GitMensch]

Thanks for the contribution; ideally we'd get MSYS2 nevs including ARM64 (using windows-11-arm runner) and other MSYS2 environments into https://github.com/Bill-Gray/PDCursesMod/blob/master/.github/workflows/github_actions_build.yml