Re: fsincos emulation on AMD CPUs

[Paolo Bonzini <pbonzini@redhat.com>]

On 12/15/2011 11:15 AM, Jan Beulich wrote:
>> >  If you really cared, perhaps fsincos can be replaced by this sequence in
>> >  the emulator:
>> >
>> >                        ; x
>> >        fld   %st       ; x x
>> >        fsin            ; x sin(x)
>> >        fxch  %st(1)    ; sin(x) x
>> >        fcos            ; sin(x) cos(x)
> I had thought of this at first too, but this is problematic in terms of
> exception handling: fpu_handle_exception() expects to see an
> exception only on the very first instruction (as it's assumed to be
> the only one), and aborts the rest of the sequence if the exception
> doesn't happen on the last instruction.

Can it just be (%0 is fic.insn_bytes):

             movb $4f-1f,%0  ; do nothing on exception here
1:          fld  %st        ; x x
             movb $3f-1f,%0  ; pop on exception here
1:          fsin            ; x sin(x)
             fxch %st(1)     ; sin(x) x
             movb $2f-1f,%0  ; xch+pop on exception here
1:          fcos            ; sin(x) cos(x)
             jmp  2f
4:          fxch %st(1)     ; x sin(x)
3:          fstp %st        ; x
2:

Paolo