mssip.h trouble

[Patrik Stridvall]

> Ah, I guess I see the problem: it doesn't really have
> anything to do with #pragma pack(), but with the default
> alignment of the 'long long' data type itself.
> 
> GCC uses a default alignment of 4 bytes for 'long long',
> so, if MSVC uses a default alignment of 8, that would be 
> the problem.

You seem to be correct.

With this code:

#ifdef _MSC_VER
typedef __int64 longlong_t;
#else
typedef __attribute__((aligned (8))) long long longlong_t;
#endif
 
GNU C now works the same as with MSVC.

> However, I think you can get GCC on i386 to use a default
> alignment of 8 for 8-byte sized types, by specifying the
> compiler option -malign-double. 

Yes, that works with GNU C as well. Even without my hack above.

> (Then you'll probably
> have to use -mpreferred-stack-boundary=3 instead of
> -mpreferred-stack-boundary=2 as well.)

It doesn't seem to do any difference in my simple example
either with -mpreferred-stack-boundary=2 or 
-mpreferred-stack-boundary=3.

The only thing that matters is whether -malign-double is set.