Le 20/07/2020 à 22:24, Segher Boessenkool a écrit :
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.
Oh nice, I was not aware that compiler may choose registers this way.
Good to know, thanks for the explanation.
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.)
Sure if the compiler can choose the registers that's far better.
Cheers,
Laurent.
