Re: Gnumach FP Struct (Beating a dead horse)

[Barry deFreese]

Samuel Thibault wrote:
> Barry deFreese, le Thu 21 Dec 2006 00:17:34 -0500, a écrit :
>   
> > I apologize for keep going on about this but I still don't quite 
> > understand why a seperate struct is needed for i386_fp_regs.
> >     
>
> I told you: this permits to easily do what is written in fpu.c:
>
>             /*
>              * Ensure that reserved parts of the environment are 0.
>              */
>             memset(user_fp_state,  0, sizeof(struct i386_fp_save));
>
>             user_fp_state->fp_control = ifps->fp_save_state.fp_control;
>             user_fp_state->fp_status  = ifps->fp_save_state.fp_status;
>             user_fp_state->fp_tag     = ifps->fp_save_state.fp_tag;
>             user_fp_state->fp_eip     = ifps->fp_save_state.fp_eip;
>             user_fp_state->fp_cs      = ifps->fp_save_state.fp_cs;
>             user_fp_state->fp_opcode  = ifps->fp_save_state.fp_opcode;
>             user_fp_state->fp_dp      = ifps->fp_save_state.fp_dp;
>             user_fp_state->fp_ds      = ifps->fp_save_state.fp_ds;
>             *user_fp_regs = ifps->fp_regs;
>
> With separate structs, the last line can be written that way, allowing
> the compiler to optimize the copy. For getting the same result without
> separate structs, we'd have to call an ugly explicit memcpy().
>
> Samuel
>
>   
Samuel,

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?

Thanks,

Barry deFreese (aka bddebian)