On 03/16/2018 04:53 PM, Richard Henderson wrote:
> We have confused the number of instructions that have been
> executed in the TB with the number of instructions needed
> to repeat the I/O instruction.
>
> We have used cpu_restore_state_from_tb, which means that
> the guest pc is pointing to the I/O instruction. The only
> time the answer to the later question is not 1 is when
> MIPS or SH4 need to re-execute the branch for the delay
> slot as well.
>
> Signed-off-by: Richard Henderson <richard.hender...@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4...@amsat.org>
> ---
> accel/tcg/translate-all.c | 21 ++++++++-------------
> 1 file changed, 8 insertions(+), 13 deletions(-)
>
> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
> index 67795cd78c..d4190602d1 100644
> --- a/accel/tcg/translate-all.c
> +++ b/accel/tcg/translate-all.c
> @@ -1736,37 +1736,32 @@ void cpu_io_recompile(CPUState *cpu, uintptr_t
> retaddr)
> cpu_abort(cpu, "cpu_io_recompile: could not find TB for pc=%p",
> (void *)retaddr);
> }
> - n = cpu->icount_decr.u16.low + tb->icount;
> cpu_restore_state_from_tb(cpu, tb, retaddr);
> - /* Calculate how many instructions had been executed before the fault
> - occurred. */
> - n = n - cpu->icount_decr.u16.low;
> - /* Generate a new TB ending on the I/O insn. */
> - n++;
> +
> /* On MIPS and SH, delay slot instructions can only be restarted if
> they were already the first instruction in the TB. If this is not
> the first instruction in a TB then re-execute the preceding
> branch. */
> + n = 1;
> #if defined(TARGET_MIPS)
> - if ((env->hflags & MIPS_HFLAG_BMASK) != 0 && n > 1) {
> + if ((env->hflags & MIPS_HFLAG_BMASK) != 0
> + && env->active_tc.PC != tb->pc) {
> env->active_tc.PC -= (env->hflags & MIPS_HFLAG_B16 ? 2 : 4);
> cpu->icount_decr.u16.low++;
> env->hflags &= ~MIPS_HFLAG_BMASK;
> + n = 2;
> }
> #elif defined(TARGET_SH4)
> if ((env->flags & ((DELAY_SLOT | DELAY_SLOT_CONDITIONAL))) != 0
> - && n > 1) {
> + && env->pc != tb->pc) {
> env->pc -= 2;
> cpu->icount_decr.u16.low++;
> env->flags &= ~(DELAY_SLOT | DELAY_SLOT_CONDITIONAL);
> + n = 2;
> }
> #endif
> - /* This should never happen. */
> - if (n > CF_COUNT_MASK) {
> - cpu_abort(cpu, "TB too big during recompile");
> - }
>
> - /* Adjust the execution state of the next TB. */
> + /* Generate a new TB executing the I/O insn. */
> cpu->cflags_next_tb = curr_cflags() | CF_LAST_IO | n;
>
> if (tb->cflags & CF_NOCACHE) {
>
