Re: [Qemu-devel] [PATCH] gdbstub: Do not kill target in system emulation mode

[Fabien Chouteau]

On 01/22/2013 03:59 PM, Jan Kiszka wrote:
> On 2013-01-22 15:04, Fabien Chouteau wrote:
>> Hello Qemu folks,
>>
>> I'm sorry to be (very) late, but I do not agree with this patch.
>>
>> Your modification just makes the "kill" command behave like "detach", so
>> why not use "detach" instead?
> 
> gdb automatically issues kill when you quite. This is where most
> casualties came from.

Hello Jan,

I asked Joel Brobecker(CC'd), a Gdb maintainer, about this issue. Here
is the answer:

On 01/23/2013 12:49 PM, Joel Brobecker wrote:
>> There's a patch in Qemu's Gdb remote server that makes the "kill"
>> command act like "detach".
>
> It seems incorrect to me. The behavior should be as follow:
>   - If the debugger was attached to an existing process, the "quit"
>     command should result in a "detach".
>   - If the debugger created the process, then "quit" should result
>     in a "kill".
>
> With that in mind, if GDB sends a "kill", it means that Qemu told
> GDB that it created the process. What it should be doing, if a "kill"
> is not the desired behavior, is to tell GDB that the process was
> attached to. For this, there is qAttached packet. See the GDB
> Users Manual, and in particular:
>
>     | `qAttached:pid'
>     | Return an indication of whether the remote server attached to an
>     | existing process or created a new process. When the multiprocess
>     | protocol extensions are supported (see multiprocess extensions), pid is
>     | an integer in hexadecimal format identifying the target process.
>     | Otherwise, gdb will omit the pid field and the query packet will be
>     | simplified as `qAttached'.  This query is used, for example, to know
>     | whether the remote process should be detached or killed when a gdb
>     | session is ended with the quit command.
>     |
>     | Reply:
>     |
>     | `1'
>     | The remote server attached to an existing process. 
>     | `0'
>     | The remote server created a new process. 
>     | `E NN'
>     | A badly formed request or an error was encountered.

qAttached is not supported in Qemu yet, this explains why Gdb sends
"kill" at the end of debug session. I will implement it and revert your
patch. Gdb will automatically detach instead of kill at the end of
debugging session.

Is that OK?

Regards,

-- 
Fabien Chouteau