Re: [PATCH] tcg/cpu-exec: precise single-stepping after an interrupt

[Luc Michel]

On 7/17/20 6:30 PM, Richard Henderson wrote:
> When single-stepping with a debugger attached to QEMU, and when an
> interrupt is raised, the debugger misses the first instruction after
> the interrupt.
>
> Buglink: https://bugs.launchpad.net/qemu/+bug/757702
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Reviewed-by: Luc Michel <luc.michel@greensocs.com>
Tested-by: Luc Michel <luc.michel@greensocs.com>

> ---
>   accel/tcg/cpu-exec.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
> index 6a3d3a3cfc..66d38f9d85 100644
> --- a/accel/tcg/cpu-exec.c
> +++ b/accel/tcg/cpu-exec.c
> @@ -588,7 +588,13 @@ static inline bool cpu_handle_interrupt(CPUState *cpu,
>           else {
>               if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
>                   replay_interrupt();
> -                cpu->exception_index = -1;
> +                /*
> +                 * After processing the interrupt, ensure an EXCP_DEBUG is
> +                 * raised when single-stepping so that GDB doesn't miss the
> +                 * next instruction.
> +                 */
> +                cpu->exception_index =
> +                    (cpu->singlestep_enabled ? EXCP_DEBUG : -1);
>                   *last_tb = NULL;
>               }
>               /* The target hook may have updated the 'cpu->interrupt_request';