tcg/cpu-exec: precise single-stepping after an interrupt

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

Richard Henderson posted 1 patch 5 years, 4 months ago

Download mbox

Test checkpatch failed

Test docker-mingw@fedora failed

Test FreeBSD passed

Test docker-quick@centos7 failed

Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/qemu tags/patchew/20200717163029.2737546-1-richard.henderson@linaro.org

Maintainers: Richard Henderson <rth@twiddle.net>, Paolo Bonzini <pbonzini@redhat.com>

accel/tcg/cpu-exec.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

Expand all Fold all

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

Posted by Richard Henderson 5 years, 4 months ago

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>
---
 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';
-- 
2.25.1

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

Posted by Luc Michel 5 years, 4 months ago

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';
>