Re: [PATCH 01/12] monitor: Clean up HMP gdbserver error reporting

["Daniel P. Berrangé" <berrange@redhat.com>]

On Fri, Aug 08, 2025 at 10:08:12AM +0200, Markus Armbruster wrote:
> HMP command gdbserver used to emit two error messages for certain
> errors.  For instance, with -M none:
> 
>     (qemu) gdbserver
>     gdbstub: meaningless to attach gdb to a machine without any CPU.
>     Could not open gdbserver on device 'tcp::1234'
> 
> The first message is the specific error, and the second one a generic
> additional message that feels superfluous to me.
> 
> Commit c0e6b8b798b (system: propagate Error to gdbserver_start (and
> other device setups)) turned the first message into a warning:
> 
>     warning: gdbstub: meaningless to attach gdb to a machine without any CPU.
>     Could not open gdbserver on device 'tcp::1234'
> 
> This is arguably worse.
> 
> hmp_gdbserver() passes &error_warn to gdbserver_start(), so that
> failure gets reported as warning, and then additionally emits the
> generic error on failure.  This is a misuse of &error_warn.
> 
> Instead, receive the error in &err and report it, as usual.  With
> this, gdbserver reports just the error:
> 
>     gdbstub: meaningless to attach gdb to a machine without any CPU.

What do you think about an alternative of removing "gdbstub: "
from all the errors raised in  'gdbserver_start' & similar, and
then using

  error_prepend(err, "Could not open gdbserver on device '%s'", device);

in hmp_gdbserver ?

I don't feel too strongly, so in any case for the patch as is,

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


> 
> Cc: Alex Bennée <alex.bennee@linaro.org>
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
>  include/exec/gdbstub.h | 3 ---
>  monitor/hmp-cmds.c     | 7 ++++---
>  2 files changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/include/exec/gdbstub.h b/include/exec/gdbstub.h
> index a16c0051ce..bd7182c4d3 100644
> --- a/include/exec/gdbstub.h
> +++ b/include/exec/gdbstub.h
> @@ -55,9 +55,6 @@ void gdb_unregister_coprocessor_all(CPUState *cpu);
>   * system emulation you can use a full chardev spec for your gdbserver
>   * port.
>   *
> - * The error handle should be either &error_fatal (for start-up) or
> - * &error_warn (for QMP/HMP initiated sessions).
> - *
>   * Returns true when server successfully started.
>   */
>  bool gdbserver_start(const char *port_or_device, Error **errp);
> diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
> index 74a0f56566..33a88ce205 100644
> --- a/monitor/hmp-cmds.c
> +++ b/monitor/hmp-cmds.c
> @@ -280,14 +280,15 @@ void hmp_log(Monitor *mon, const QDict *qdict)
>  
>  void hmp_gdbserver(Monitor *mon, const QDict *qdict)
>  {
> +    Error *err = NULL;
>      const char *device = qdict_get_try_str(qdict, "device");
> +
>      if (!device) {
>          device = "tcp::" DEFAULT_GDBSTUB_PORT;
>      }
>  
> -    if (!gdbserver_start(device, &error_warn)) {
> -        monitor_printf(mon, "Could not open gdbserver on device '%s'\n",
> -                       device);
> +    if (!gdbserver_start(device, &err)) {
> +        error_report_err(err);
>      } else if (strcmp(device, "none") == 0) {
>          monitor_printf(mon, "Disabled gdbserver\n");
>      } else {
> -- 
> 2.49.0
> 
> 

With regards,
Daniel
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