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.
Segher
