On Mon, Jul 20, 2020 at 03:10:41PM -0500, Segher Boessenkool wrote:
> On Mon, Jul 20, 2020 at 11:39:56AM +0200, Laurent Dufour wrote:
> > Le 16/07/2020 à 10:32, Ram Pai a écrit :
> > >+ if (is_secure_guest()) { \
> > >+ __asm__ __volatile__("mfsprg0 %3;" \
> > >+ "lnia %2;" \
> > >+ "ld %2,12(%2);" \
> > >+ "mtsprg0 %2;" \
> > >+ "sync;" \
> > >+ #insn" %0,%y1;" \
> > >+ "twi 0,%0,0;" \
> > >+ "isync;" \
> > >+ "mtsprg0 %3" \
> > >+ : "=r" (ret) \
> > >+ : "Z" (*addr), "r" (0), "r" (0) \
> >
> > I'm wondering if SPRG0 is restored to its original value.
> > You're using the same register (r0) for parameters 2 and 3, so when doing
> > lnia %2, you're overwriting the SPRG0 value you saved in r0 just earlier.
>
> It is putting the value 0 in the registers the compiler chooses for
> operands 2 and 3. But operand 3 is written, while the asm says it is an
> input. It needs an earlyclobber as well.
>
> > It may be clearer to use explicit registers for %2 and %3 and to mark them
> > as modified for the compiler.
>
> That is not a good idea, imnsho.
(The explicit register number part, I mean; operand 2 should be an
output as well, yes.)
Segher
