On 14:26 Mon 14 Feb , Luc Michel wrote:
> In some cases, cpu->exit_request can be false after handling the
> interrupt, leading to another TB being executed instead of returning
> to the main loop.
>
> Fix this by returning true unconditionally when in single-step mode.
>
> Fixes: ba3c35d9c4026361fd380b269dc6def9510b7166
>
> Signed-off-by: Luc Michel <[email protected]>
Hi Richard, did you have time to have a look at this patch?
Thanks,
Luc
> ---
> Coming back on this issue I worked on with Richard in 2020. The issue is
> that when debugging the guest with GDB, the first instruction of the IRQ
> handler is missed by GDB (it's still executed though).
>
> It happened to me again in TCG RR mode (but not in MTTCG). It seems that
> cpu->exit_request can be false in RR mode when returning from
> cc->tcg_ops->cpu_exec_interrupt, leading to cpu_handle_interrupt
> returning false and the next TB being executed, instead of the EXCP_DEBUG
> being handled.
> ---
> accel/tcg/cpu-exec.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
> index 8b4cd6c59d..74d7f83f34 100644
> --- a/accel/tcg/cpu-exec.c
> +++ b/accel/tcg/cpu-exec.c
> @@ -796,13 +796,17 @@ static inline bool cpu_handle_interrupt(CPUState *cpu,
> /*
> * 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;
> + if (unlikely(cpu->singlestep_enabled)) {
> + cpu->exception_index = EXCP_DEBUG;
> + return true;
> + } else {
> + cpu->exception_index = -1;
> + *last_tb = NULL;
> + }
> }
> /* The target hook may have updated the 'cpu->interrupt_request';
> * reload the 'interrupt_request' value */
> interrupt_request = cpu->interrupt_request;
> }
> --
> 2.17.1
>
--
