Re: Gnumach FP Struct (Beating a dead horse)

[Samuel Thibault]

Barry deFreese, le Thu 21 Dec 2006 09:54:05 -0500, a écrit :
> OK, that makes sense, sorry.  It just takes a while to get through my 
> thick skull sometimes.  So about my question about adding a struct for 
> the fxsr stuff.  I don't really want to add a union of 4 structs right, 
> I need two unions of two structs?  So I'd have something like this:
> 
> union i387_save_struct {
>    struct i386_fp_save;
>    struct i386_fpxsr_save;
> }
> 
> and
> 
> union i387_regs_struct {
>    struct i386_fp_regs;
>    struct i386_fpxsr_regs;
> }
> 
> 
> Make sense?

Makes sense, but won't work. Remember that the size of a union is the
size of its biggest member. When you'll put both unions one after the
other in the i386_fpsave_state structure, i386_fp_regs will _not_
be just after i386_fp_save, just because sizeof(i386_fpxsr_save) >
sizeof(i386_fp_save). The union has hence to be before the split into
structures.

Also, about structure, look at the Intel docs: only the XMM register
saving area doesn't have holes.

Samuel