Patchwork [1/2] Add GDB qAttached support

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Submitter Fabien Chouteau
Date March 5, 2013, 4:03 p.m.
Message ID <1362499399-19475-1-git-send-email-chouteau@adacore.com>
Download mbox | patch
Permalink /patch/225068/
State New
Headers show

Comments

Fabien Chouteau - March 5, 2013, 4:03 p.m.
With this patch GDB will issue a "detach" command at the end of a
debugging session instead of a "kill". This behavior can be inverted
with the new option -gdb-not-attached.

This patch implements the requirement described in Jan Kiszka's patch:
"gdbstub: Do not kill target in system emulation mode". The patch can
therefore be reverted.

Signed-off-by: Fabien Chouteau <chouteau@adacore.com>
---
 gdbstub.c              |   13 ++++++++++++-
 include/exec/gdbstub.h |    2 ++
 qemu-options.hx        |    7 +++++++
 vl.c                   |    3 +++
 4 files changed, 24 insertions(+), 1 deletion(-)
Jan Kiszka - March 10, 2013, 8:06 a.m.
On 2013-03-05 17:03, Fabien Chouteau wrote:
> With this patch GDB will issue a "detach" command at the end of a
> debugging session instead of a "kill". This behavior can be inverted
> with the new option -gdb-not-attached.
> 
> This patch implements the requirement described in Jan Kiszka's patch:
> "gdbstub: Do not kill target in system emulation mode". The patch can
> therefore be reverted.
> 
> Signed-off-by: Fabien Chouteau <chouteau@adacore.com>
> ---
>  gdbstub.c              |   13 ++++++++++++-
>  include/exec/gdbstub.h |    2 ++
>  qemu-options.hx        |    7 +++++++
>  vl.c                   |    3 +++
>  4 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/gdbstub.c b/gdbstub.c
> index e414ad9..c0686a9 100644
> --- a/gdbstub.c
> +++ b/gdbstub.c
> @@ -32,7 +32,6 @@
>  #include "monitor/monitor.h"
>  #include "char/char.h"
>  #include "sysemu/sysemu.h"
> -#include "exec/gdbstub.h"
>  #endif
>  
>  #define MAX_PACKET_LENGTH 4096
> @@ -41,6 +40,9 @@
>  #include "qemu/sockets.h"
>  #include "sysemu/kvm.h"
>  #include "qemu/bitops.h"
> +#include "exec/gdbstub.h"
> +
> +static bool gdb_attached = true;
>  
>  #ifndef TARGET_CPU_MEMORY_RW_DEBUG
>  static inline int target_memory_rw_debug(CPUArchState *env, target_ulong addr,
> @@ -2491,6 +2493,10 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
>              break;
>          }
>  #endif
> +        if (strncmp(p, "Attached", 8) == 0) {
> +            put_packet(s, gdb_attached ? "1" : "0");
> +            break;
> +        }

This works as expected for system mode, but now inverts the behaviour
for user mode - that's unexpected and not ok.

>          /* Unrecognised 'q' command.  */
>          goto unknown_command;
>  
> @@ -3055,3 +3061,8 @@ int gdbserver_start(const char *device)
>      return 0;
>  }
>  #endif
> +
> +void gdb_set_attached(bool attached)
> +{
> +    gdb_attached = attached;
> +}
> diff --git a/include/exec/gdbstub.h b/include/exec/gdbstub.h
> index ba20afa..b2d3b13 100644
> --- a/include/exec/gdbstub.h
> +++ b/include/exec/gdbstub.h
> @@ -50,4 +50,6 @@ int gdbserver_start(const char *port);
>  /* in gdbstub-xml.c, generated by scripts/feature_to_c.sh */
>  extern const char *const xml_builtin[][2];
>  
> +void gdb_set_attached(bool attached);
> +
>  #endif
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 6f9334a..026d3eb 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -2988,6 +2988,13 @@ property must be set.  These objects are placed in the
>  '/objects' path.
>  ETEXI
>  
> +DEF("gdb-not-attached", 0, QEMU_OPTION_gdb_not_attached,
> +    "-gdb-not-attached\n"
> +    "                Do not set Gdb remote server in attached mode.\n"
> +    "                When exiting debugging session, Gdb will send a 'kill'\n"
> +    "                command instead of a 'detach'.\n",
> +    QEMU_ARCH_ALL)
> +

First of all, why do we need this configurable? In which use cases do
you want attached mode for user emulation or kill mode for system
emulation/virtualization?

Then, if you can convince us that such a switch is useful, a new
top-level command line option is still a no-go. We already have -gdb, so
this would have to become an option to it.

In any case, I would suggest to add static attached mode first (enabled
for system, disable for user), revert my patch and then, optionally,
propose an attached mode control.

Jan
Fabien Chouteau - March 11, 2013, 11:22 a.m.
On 03/10/2013 09:06 AM, Jan Kiszka wrote:
>> @@ -2491,6 +2493,10 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
>>              break;
>>          }
>>  #endif
>> +        if (strncmp(p, "Attached", 8) == 0) {
>> +            put_packet(s, gdb_attached ? "1" : "0");
>> +            break;
>> +        }
>
> This works as expected for system mode, but now inverts the behaviour
> for user mode - that's unexpected and not ok.
>

OK, I can change the default value for user mode.

>> diff --git a/qemu-options.hx b/qemu-options.hx
>> index 6f9334a..026d3eb 100644
>> --- a/qemu-options.hx
>> +++ b/qemu-options.hx
>> @@ -2988,6 +2988,13 @@ property must be set.  These objects are placed in the
>>  '/objects' path.
>>  ETEXI
>>
>> +DEF("gdb-not-attached", 0, QEMU_OPTION_gdb_not_attached,
>> +    "-gdb-not-attached\n"
>> +    "                Do not set Gdb remote server in attached mode.\n"
>> +    "                When exiting debugging session, Gdb will send a 'kill'\n"
>> +    "                command instead of a 'detach'.\n",
>> +    QEMU_ARCH_ALL)
>> +
>
> First of all, why do we need this configurable? In which use cases do
> you want attached mode for user emulation or kill mode for system
> emulation/virtualization?
>

It's more convenient for us, we expect QEMU to terminate at the end of
debugging session because we do not run big systems/kernels but short
test programs. It used to be the default behavior of QEMU, and our
test-suites, IDE, developers and users are expecting this.

> Then, if you can convince us that such a switch is useful, a new
> top-level command line option is still a no-go. We already have -gdb, so
> this would have to become an option to it.
>

Something like:

-gdb dev[,attached=on|off]        wait for gdb connection on 'dev'

This will not fit nicely in the current option because 'dev' is a
chardev descriptor. I will have to add 'attached' in the list of chardev
opts, which is not correct. Or do some nasty strings manipulation.

Maybe this:

-gdb-opts attached=on|off

We can extend it latter if more options are needed.

> In any case, I would suggest to add static attached mode first (enabled
> for system, disable for user), revert my patch and then, optionally,
> propose an attached mode control.
>

Mode control is not optional for me.

Regards,
Jan Kiszka - March 11, 2013, 11:36 a.m.
On 2013-03-11 12:22, Fabien Chouteau wrote:
> On 03/10/2013 09:06 AM, Jan Kiszka wrote:
>>> @@ -2491,6 +2493,10 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
>>>              break;
>>>          }
>>>  #endif
>>> +        if (strncmp(p, "Attached", 8) == 0) {
>>> +            put_packet(s, gdb_attached ? "1" : "0");
>>> +            break;
>>> +        }
>>
>> This works as expected for system mode, but now inverts the behaviour
>> for user mode - that's unexpected and not ok.
>>
> 
> OK, I can change the default value for user mode.
> 
>>> diff --git a/qemu-options.hx b/qemu-options.hx
>>> index 6f9334a..026d3eb 100644
>>> --- a/qemu-options.hx
>>> +++ b/qemu-options.hx
>>> @@ -2988,6 +2988,13 @@ property must be set.  These objects are placed in the
>>>  '/objects' path.
>>>  ETEXI
>>>
>>> +DEF("gdb-not-attached", 0, QEMU_OPTION_gdb_not_attached,
>>> +    "-gdb-not-attached\n"
>>> +    "                Do not set Gdb remote server in attached mode.\n"
>>> +    "                When exiting debugging session, Gdb will send a 'kill'\n"
>>> +    "                command instead of a 'detach'.\n",
>>> +    QEMU_ARCH_ALL)
>>> +
>>
>> First of all, why do we need this configurable? In which use cases do
>> you want attached mode for user emulation or kill mode for system
>> emulation/virtualization?
>>
> 
> It's more convenient for us, we expect QEMU to terminate at the end of
> debugging session because we do not run big systems/kernels but short
> test programs. It used to be the default behavior of QEMU, and our
> test-suites, IDE, developers and users are expecting this.

And it's not possible to replace 'q' with 'k' in your gdb control
scripts? That gives you a well-defined behaviour, and we don't need to
tweak QEMU, specifically its command line, for this special case.

Jan
Fabien Chouteau - March 11, 2013, 11:59 a.m.
On 03/11/2013 12:36 PM, Jan Kiszka wrote:
> On 2013-03-11 12:22, Fabien Chouteau wrote:
>> On 03/10/2013 09:06 AM, Jan Kiszka wrote:
>>>> diff --git a/qemu-options.hx b/qemu-options.hx
>>>> index 6f9334a..026d3eb 100644
>>>> --- a/qemu-options.hx
>>>> +++ b/qemu-options.hx
>>>> @@ -2988,6 +2988,13 @@ property must be set.  These objects are placed in the
>>>>  '/objects' path.
>>>>  ETEXI
>>>>
>>>> +DEF("gdb-not-attached", 0, QEMU_OPTION_gdb_not_attached,
>>>> +    "-gdb-not-attached\n"
>>>> +    "                Do not set Gdb remote server in attached mode.\n"
>>>> +    "                When exiting debugging session, Gdb will send a 'kill'\n"
>>>> +    "                command instead of a 'detach'.\n",
>>>> +    QEMU_ARCH_ALL)
>>>> +
>>>
>>> First of all, why do we need this configurable? In which use cases do
>>> you want attached mode for user emulation or kill mode for system
>>> emulation/virtualization?
>>>
>>
>> It's more convenient for us, we expect QEMU to terminate at the end of
>> debugging session because we do not run big systems/kernels but short
>> test programs. It used to be the default behavior of QEMU, and our
>> test-suites, IDE, developers and users are expecting this.
>
> And it's not possible to replace 'q' with 'k' in your gdb control
> scripts?

It's not just in a script or two, as I said it's test-suites, IDE,
developers and users.

> That gives you a well-defined behaviour, and we don't need to
> tweak QEMU, specifically its command line, for this special case.
>

I don't understand the issue with this new option.

Regards,

Patch

diff --git a/gdbstub.c b/gdbstub.c
index e414ad9..c0686a9 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -32,7 +32,6 @@ 
 #include "monitor/monitor.h"
 #include "char/char.h"
 #include "sysemu/sysemu.h"
-#include "exec/gdbstub.h"
 #endif
 
 #define MAX_PACKET_LENGTH 4096
@@ -41,6 +40,9 @@ 
 #include "qemu/sockets.h"
 #include "sysemu/kvm.h"
 #include "qemu/bitops.h"
+#include "exec/gdbstub.h"
+
+static bool gdb_attached = true;
 
 #ifndef TARGET_CPU_MEMORY_RW_DEBUG
 static inline int target_memory_rw_debug(CPUArchState *env, target_ulong addr,
@@ -2491,6 +2493,10 @@  static int gdb_handle_packet(GDBState *s, const char *line_buf)
             break;
         }
 #endif
+        if (strncmp(p, "Attached", 8) == 0) {
+            put_packet(s, gdb_attached ? "1" : "0");
+            break;
+        }
         /* Unrecognised 'q' command.  */
         goto unknown_command;
 
@@ -3055,3 +3061,8 @@  int gdbserver_start(const char *device)
     return 0;
 }
 #endif
+
+void gdb_set_attached(bool attached)
+{
+    gdb_attached = attached;
+}
diff --git a/include/exec/gdbstub.h b/include/exec/gdbstub.h
index ba20afa..b2d3b13 100644
--- a/include/exec/gdbstub.h
+++ b/include/exec/gdbstub.h
@@ -50,4 +50,6 @@  int gdbserver_start(const char *port);
 /* in gdbstub-xml.c, generated by scripts/feature_to_c.sh */
 extern const char *const xml_builtin[][2];
 
+void gdb_set_attached(bool attached);
+
 #endif
diff --git a/qemu-options.hx b/qemu-options.hx
index 6f9334a..026d3eb 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2988,6 +2988,13 @@  property must be set.  These objects are placed in the
 '/objects' path.
 ETEXI
 
+DEF("gdb-not-attached", 0, QEMU_OPTION_gdb_not_attached,
+    "-gdb-not-attached\n"
+    "                Do not set Gdb remote server in attached mode.\n"
+    "                When exiting debugging session, Gdb will send a 'kill'\n"
+    "                command instead of a 'detach'.\n",
+    QEMU_ARCH_ALL)
+
 HXCOMM This is the last statement. Insert new options before this line!
 STEXI
 @end table
diff --git a/vl.c b/vl.c
index c03edf1..ccd7405 100644
--- a/vl.c
+++ b/vl.c
@@ -3815,6 +3815,9 @@  int main(int argc, char **argv, char **envp)
                     exit(1);
                 }
                 break;
+            case QEMU_OPTION_gdb_not_attached:
+                gdb_set_attached(false);
+                break;
             default:
                 os_parse_cmd_args(popt->index, optarg);
             }