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

[陳韋任]

On Fri, Feb 10, 2012 at 08:14:41AM +0000, Stefan Hajnoczi wrote:
> On Thu, Feb 09, 2012 at 06:33:16PM +0800, 陳韋任 wrote:
> >   The question is not so related to QEMU itself, but I want to give it a 
> > try.
> > 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, but 
> > the
> > GDB command `set follow-fork-mode child` doesn't work. This seems to be a 
> > bug
> > or missing feature in GDB remote protocol. [1]
> > 
> >   Is there a way to do what I'm trying to do? Thanks!
> 
> I'm confused.  If you are running a system emulator with a guest OS
> inside then GDB's process-level features are not available.  The QEMU
> gdbstub gives you access at the system-level.  If you want to debug
> guest processes, run gdb inside the guest.

  Hope the code snip below can clarify what I am trying to do.

----------------- 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, but it seems that GDB
stick with task 0 and cannot follow task 1 even I do `set follow-fork-mode
child`.

  Thanks! 

Regards,
chenwj

-- 
Wei-Ren Chen (陳韋任)
Computer Systems Lab, Institute of Information Science,
Academia Sinica, Taiwan (R.O.C.)
Tel:886-2-2788-3799 #1667
Homepage: http://people.cs.nctu.edu.tw/~chenwj