Re: [Qemu-devel] How to follow a child process created in the guest OS?

[Stefan Hajnoczi]

On Sun, Feb 12, 2012 at 3:00 AM, Wei Yang <address@hidden> wrote:
> 2012/2/11 malc <address@hidden>:
>> On Sat, 11 Feb 2012, Andreas F?rber wrote:
>>
>>> Am 10.02.2012 11:26, schrieb ???:
>>> > On Fri, Feb 10, 2012 at 08:14:41AM +0000, Stefan Hajnoczi wrote:
>>> >> On Thu, Feb 09, 2012 at 06:33:16PM +0800, ??? wrote:
>>> >>> I am running a tiny OS on QEMU and debugging it with gdbstub. The tiny 
>>> >>> OS will
>>> >>> fork process 1, 2, ... and so on. I want to follow the child process, 
>>> >>> [...]
>>> >>>
>>> >>>   Is there a way to do what I'm trying to do? Thanks!
>>>
>>> > ----------------- Tiny OS code -----------------------------
>>> > void main(void)   /* This really IS void, no error here. */
>>> > {
>>> >   /* initialize enviroment */
>>> >
>>> >   sti();
>>> >   move_to_user_mode();
>>> >   if (!fork()) {    /* we count on this going ok */
>>> >     init();         // task 1
>>> >   }
>>> >
>>> >   for(;;) pause();  // task 0
>>> > }
>>> > ------------------------------------------------------------
>>> >
>>> >   I am running this tiny OS on QEMU then using GDB to connect it.
>>> > I want to follow task 1 after the forking, [...]
>>>
>
> Could the Qemu gdbstub debug a user space process?

What people have been trying to explain is that, yes, gdbstub can
debug user space processes but not in an easy way.  It's like using a
bicycle to travel from Paris to Beijing - it takes a lot of time and
effort, you may want to catch a plane instead.

The QEMU gdbstub is a hardware-level debugger.  It shows you what the
CPU is doing.  It does not know about processes.  Of course, if *you*
understand how processes are implemented in this operating systems,
*you* could do all the process-level debugging yourself without the
help of the debugger.

Stefan