[uml-devel] uml and gdb debugging questions

[uml-devel] uml and gdb debugging questions

[Miao Qingjun]

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Hi,

I have several problems about uml-2.6.17 and gdb debugging.

I start "gdb uml", "b sys_init_module", then "run",
but gdb is not break at sys_init_module() when I insmod LKM?
Why? How can I do it?


When I type control-c in gdb, the virtual console xterm is also closed,
I just want to enter gdb command line to single step kernel code, how can I do it?


thanks!

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Re: [uml-devel] uml and gdb debugging questions

[Blaisorblade]

On Wednesday 12 July 2006 03:05, Miao Qingjun wrote:
> Hi,
>
> I have several problems about uml-2.6.17 and gdb debugging.
>
> I start "gdb uml", "b sys_init_module", then "run",
> but gdb is not break at sys_init_module() when I insmod LKM?
> Why? How can I do it?
Sometimes breakpoints don't work in GDB :-(. An hack was posted: it was based 
on recompiling after adding code calling pause() if a variable was set and 
setting the variable only from the debugger; however some special care was 
needed to avoid gcc recognizing nobody set the variable and optimizing the 
check out.
> When I type control-c in gdb, the virtual console xterm is also closed,
This doesn't happen here for what I remember, I used both Ctrl-C and kill -INT 
<main pid> to get back the control in the console.
> I just want to enter gdb command line to single step kernel code, how can I
> do it?

-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade
Chiacchiera con i tuoi amici in tempo reale! 
 http://it.yahoo.com/mail_it/foot/*http://it.messenger.yahoo.com 



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Re: [uml-devel] [uml-user] uml and gdb debugging questions

[Jeff Dike]

On Wed, Jul 12, 2006 at 09:05:22AM +0800, Miao Qingjun wrote:
> I start "gdb uml", "b sys_init_module", then "run",
> but gdb is not break at sys_init_module() when I insmod LKM?
> Why? How can I do it?

Some versions of gdb don't work well on UML.  One thing that often
works is to attach to UML when it's booted, just before doing whatever
you want to debug.

				Jeff

> When I type control-c in gdb, the virtual console xterm is also
> closed,

How are you running UML?  You normally can't ^C to get back to gdb
because the UML console has put the terminal in raw mode, so it can
see ^C, ^Z, etc and pass them along to the UML foreground process.

What I normally do is kill -INT <pid>, where pid is the lowest UML
pid.

				Jeff


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Re: [uml-devel] [uml-user] uml and gdb debugging questions

[Blaisorblade]

On Thursday 13 July 2006 21:37, Jeff Dike wrote:
> On Wed, Jul 12, 2006 at 09:05:22AM +0800, Miao Qingjun wrote:
> > I start "gdb uml", "b sys_init_module", then "run",
> > but gdb is not break at sys_init_module() when I insmod LKM?
> > Why? How can I do it?
>
> Some versions of gdb don't work well on UML.  One thing that often
> works is to attach to UML when it's booted, just before doing whatever
> you want to debug.
>
> 				Jeff
>
> > When I type control-c in gdb, the virtual console xterm is also
> > closed,
>
> How are you running UML?  You normally can't ^C to get back to gdb
> because the UML console has put the terminal in raw mode, so it can
> see ^C, ^Z, etc and pass them along to the UML foreground process.
>
> What I normally do is kill -INT <pid>, where pid is the lowest UML
> pid.
I forgot one note - I either attach gdb to UML after boot or boot it with con0 
redirected away from fd:0,fd:1.
And I often find that setting a breakpoint after UML has fully booted works 
better than setting it before boot. A lot better.

-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade
Chiacchiera con i tuoi amici in tempo reale! 
 http://it.yahoo.com/mail_it/foot/*http://it.messenger.yahoo.com 



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