Re: [Qemu-devel] [PATCH] tests/tcg: add test-i386-fprem and make target for comparing QEMU to h/w

[Catalin Patulea]

On Tue, Jul 17, 2012 at 8:23 AM, Peter Maydell <address@hidden> wrote:
> I think our current position is "don't use bitfields for anything that
> has to match an externally defined layout". This is because on Windows
> we have to compile with -mms-bitfields [for compatibility with Windows
> APIs], which can lead to different layouts for structs with bitfields.
> For instance in your struct:
>
>> +    struct {
>> +        unsigned long long mantissa:63;
>> +        unsigned int one:1;
>> +        unsigned int exponent:15;
>> +        unsigned int negative:1;
>> +        unsigned int empty:16;
>> +    } ieee;
>
> the Windows build would not put the fields 'mantissa' and
> 'one' in the same 64 bit word, it would insert a padding bit.
Since floatx80 is not part of a Windows API (in fact, it's not part of
any API, it's in a test), could I give the structs an attribute of
"gcc_struct"?

http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html (under
"6.36.5 i386 Variable Attributes")