Re: [Qemu-devel] [PATCH v3 35/45] windbg: debug exception subscribing

[Ladi Prosek <lprosek@redhat.com>]

On Tue, Nov 21, 2017 at 3:10 PM, Mihail Abakumov
<mikhail.abakumov@ispras.ru> wrote:
> Added handler registration of gdb debug exception. Its exception also can be used for windbg.
>
> Signed-off-by: Mihail Abakumov <mikhail.abakumov@ispras.ru>
> Signed-off-by: Pavel Dovgalyuk <dovgaluk@ispras.ru>
> Signed-off-by: Dmitriy Koltunov <koltunov@ispras.ru>
> ---
>  cpus.c                  |   18 +++++++++++++++++-
>  gdbstub.c               |    4 ++++
>  include/sysemu/sysemu.h |    2 ++
>  windbgstub.c            |   16 ++++++++++++----
>  4 files changed, 35 insertions(+), 5 deletions(-)
>
> diff --git a/cpus.c b/cpus.c
> index 9bed61eefc..212553b7e3 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -77,6 +77,8 @@ int64_t max_advance;
>  static QEMUTimer *throttle_timer;
>  static unsigned int throttle_percentage;
>
> +static void (*excp_debug_handler)(CPUState *cpu);
> +
>  #define CPU_THROTTLE_PCT_MIN 1
>  #define CPU_THROTTLE_PCT_MAX 99
>  #define CPU_THROTTLE_TIMESLICE_NS 10000000
> @@ -960,9 +962,23 @@ static bool cpu_can_run(CPUState *cpu)
>      return true;
>  }
>
> +bool register_excp_debug_handler(void (*handler)(CPUState *cpu))
> +{
> +    if (excp_debug_handler == NULL) {
> +        excp_debug_handler = handler;
> +        return true;
> +    } else {
> +        error_report("ERROR: Something debugger already using");

So I take it that -windbg and -gdb cannot be used at the same time.
Should it be handled in a more explicit way with a more user-friendly
error?

Right now I get this error, which is more like an implementation
detail (could the debug handler be refactored into a multicast event
in the future?) and does not even make sense as a sentence.

> +        return false;
> +    }
> +}
> +
>  static void cpu_handle_guest_debug(CPUState *cpu)
>  {
> -    gdb_set_stop_cpu(cpu);
> +    if (excp_debug_handler != NULL) {
> +        excp_debug_handler(cpu);
> +    }
> +
>      qemu_system_debug_request();
>      cpu->stopped = true;
>  }
> diff --git a/gdbstub.c b/gdbstub.c
> index 2a94030d3b..8c76f54117 100644
> --- a/gdbstub.c
> +++ b/gdbstub.c
> @@ -2006,6 +2006,10 @@ int gdbserver_start(const char *device)
>      s->mon_chr = mon_chr;
>      s->current_syscall_cb = NULL;
>
> +    if (!register_excp_debug_handler(gdb_set_stop_cpu)) {
> +        exit(1);
> +    }
> +
>      return 0;
>  }
>
> diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
> index b21369672a..34588c99b4 100644
> --- a/include/sysemu/sysemu.h
> +++ b/include/sysemu/sysemu.h
> @@ -193,6 +193,8 @@ QemuOpts *qemu_get_machine_opts(void);
>
>  bool defaults_enabled(void);
>
> +bool register_excp_debug_handler(void (*handler)(CPUState *cpu));
> +
>  extern QemuOptsList qemu_legacy_drive_opts;
>  extern QemuOptsList qemu_common_drive_opts;
>  extern QemuOptsList qemu_drive_opts;
> diff --git a/windbgstub.c b/windbgstub.c
> index 489abe6d6c..b33f412659 100755
> --- a/windbgstub.c
> +++ b/windbgstub.c
> @@ -115,16 +115,20 @@ static void windbg_send_control_packet(uint16_t type)
>      windbg_state->ctrl_packet_id ^= 1;
>  }
>
> -static void windbg_vm_stop(void)
> +static void windbg_bp_handler(CPUState *cpu)
>  {
> -    CPUState *cpu = qemu_get_cpu(0);
> -    vm_stop(RUN_STATE_PAUSED);
> -
>      SizedBuf buf = kd_gen_exception_sc(cpu);
>      windbg_send_data_packet(buf.data, buf.size, PACKET_TYPE_KD_STATE_CHANGE64);
>      SBUF_FREE(buf);
>  }
>
> +static void windbg_vm_stop(void)
> +{
> +    CPUState *cpu = qemu_get_cpu(0);
> +    vm_stop(RUN_STATE_PAUSED);
> +    windbg_bp_handler(cpu);
> +}
> +
>  static void windbg_process_manipulate_packet(ParsingContext *ctx)
>  {
>      CPUState *cpu;
> @@ -432,6 +436,10 @@ int windbg_server_start(const char *device)
>
>      qemu_register_reset(windbg_handle_reset, NULL);
>
> +    if (!register_excp_debug_handler(windbg_bp_handler)) {
> +        exit(1);
> +    }
> +
>      atexit(windbg_exit);
>      return 0;
>  }
>