[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [RFC PATCH] tcg/cpu-exec: precise single-stepping after an exception
From: |
Peter Maydell |
Subject: |
Re: [RFC PATCH] tcg/cpu-exec: precise single-stepping after an exception |
Date: |
Thu, 16 Jul 2020 21:12:27 +0100 |
On Thu, 16 Jul 2020 at 11:08, Luc Michel <luc.michel@greensocs.com> wrote:
>
> When single-stepping with a debugger attached to QEMU, and when an
> exception is raised, the debugger misses the first instruction after the
> exception:
This is a long-standing bug; thanks for looking at it.
(https://bugs.launchpad.net/qemu/+bug/757702)
> diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
> index d95c4848a4..e85fab5d40 100644
> --- a/accel/tcg/cpu-exec.c
> +++ b/accel/tcg/cpu-exec.c
> @@ -502,10 +502,21 @@ static inline bool cpu_handle_exception(CPUState *cpu,
> int *ret)
> CPUClass *cc = CPU_GET_CLASS(cpu);
> qemu_mutex_lock_iothread();
> cc->do_interrupt(cpu);
> qemu_mutex_unlock_iothread();
> cpu->exception_index = -1;
> +
> + if (unlikely(cpu->singlestep_enabled)) {
> + /*
> + * After processing the exception, ensure an EXCP_DEBUG is
> + * raised when single-stepping so that GDB doesn't miss the
> + * next instruction.
> + */
> + cpu->exception_index = EXCP_DEBUG;
> + return cpu_handle_exception(cpu, ret);
> + }
I like the idea of being able to do this generically in
the main loop.
How about interrupts? If we are single-stepping and we
take an interrupt I guess we want to stop before the first
insn of the interrupt handler rather than after it, which
would imply a similar change to cpu_handle_interrupt().
thanks
-- PMM