On 31/10/2017 12:26, Pavel Dovgalyuk wrote:
> This patch resets icount_decr.u32.high before calling cpu_exec_nocache
> when exception is pending. Exception is caused by the first instruction
> in the block and it cannot be executed without resetting the flag.
>
> Signed-off-by: Maria Klimushenkova <maria.klimushenk...@ispras.ru>
> Signed-off-by: Pavel Dovgalyuk <pavel.dovga...@ispras.ru>
>
> ---
> accel/tcg/cpu-exec.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
> index 35d0240..aaa9c2d 100644
> --- a/accel/tcg/cpu-exec.c
> +++ b/accel/tcg/cpu-exec.c
> @@ -500,6 +500,7 @@ static inline bool cpu_handle_exception(CPUState *cpu,
> int *ret)
> } else if (replay_has_exception()
> && cpu->icount_decr.u16.low + cpu->icount_extra == 0) {
> /* try to cause an exception pending in the log */
> + atomic_set(&cpu->icount_decr.u16.high, 0);
> cpu_exec_nocache(cpu, 1, tb_find(cpu, NULL, 0, curr_cflags()), true);
> *ret = -1;
> return true;
>
I am not sure about this. I think if instead you should return false
from here and EXCP_INTERRUPT from cpu_exec.
More important: there is still a race, because high can be set to -1
right after your atomic_set. Maybe:
1) you should only return true if cpu->exception_index was set by
cpu_exec_nocache?
2) you should not do
*ret = -1;
return true;
and instead do
if (cpu->exception_index < 0 &&
replay_has_exception() &&
cpu->icount_decr.u16.low + cpu->icount_extra == 0) {
/* try to cause an exception pending in the log */
cpu_exec_nocache(cpu, 1, tb_find(cpu, NULL, 0, curr_cflags()), true);
}
}
if (cpu->exception_index >= 0) {
...
}
return false;
Paolo
