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.

Cc: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@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

On 23/9/25 11:09, 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'

Orthogonal to this patch: interesting. This comes from commit
508b4ecc393 ("gdbstub.c: fix GDB connection segfault caused by empty
machines"). This feels wrong to me, as it is OK to use a jtag probe
to access memory or program a flash, even without any cpu online.

Yet another side-effect of use of the ill-first_cpu global variable.

Back to this patch description, probably not the best error example =)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> 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.
> 
> Cc: Alex Bennée <alex.bennee@linaro.org>
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
> ---
>   include/exec/gdbstub.h | 3 ---
>   monitor/hmp-cmds.c     | 7 ++++---
>   2 files changed, 4 insertions(+), 6 deletions(-)

Philippe Mathieu-Daudé <philmd@linaro.org> writes:

> On 23/9/25 11:09, 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'
>
> Orthogonal to this patch: interesting. This comes from commit
> 508b4ecc393 ("gdbstub.c: fix GDB connection segfault caused by empty
> machines"). This feels wrong to me, as it is OK to use a jtag probe
> to access memory or program a flash, even without any cpu online.
>
> Yet another side-effect of use of the ill-first_cpu global variable.
>
> Back to this patch description, probably not the best error example =)

I picked it because how to trigger it was obvious to me.

Happy to use another one if you show it to me :)

> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

Thanks!