ps at leissner.se
Tue Sep 10 13:37:18 CDT 2002
> 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:
typedef __int64 longlong_t;
typedef __attribute__((aligned (8))) long long longlong_t;
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
The only thing that matters is whether -malign-double is set.
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