On 10/05/2010 07:27 PM, Thawan Kooburat wrote:
> Hi,
>
> I am using kernel 2.6.35.5 and I am trying to debug the kernel while
> it is resuming from hibernate (using TuxOnIce).
>
> I am able to attach gdb to the "boot" kernel and trace its operations
> normally. However, when the boot kernel finished restoring the
> "resume" kernel, gdb seems to lose track of the kernel and I can no
> longer use gdb after this point.
>
> The boot kernel restore the resume kernel by loading it from a disk.
> When it ready to "jumps" into the resume kernel, it will relocate
> resume kernel's memory pages over itself. I guess that this is the
> reason why I cannot use gdb after the resume kernel start executing.
>
> Is it possible to insert kgdb_breakpoint(); into kernel's resume path?
> so that I can attach gdb as soon as the resume kernel start executing.
>
I would assume you can, you probably just need the address. Also you
could force the kernel into the kernel debugger in the resume path by
simply compiling in a breakpoint, or making a kprobe that installs a
breakpoint in the worst case scenario.
To do so:
#include <linux/kgdb.h>
void some_resume_function(void)
{
...
kgdb_breakpoint();
...
}
> I am working inside KVM and I can still get printk() message via
> virtual serial port as soon as the resume kernel comes back. Does this
> means that there is enough I/O facility for KGDB to start working at
> this point?
>
If you can see printk messages, enough of the kernel is alive that you
would be able to use the kernel debugger.
If you are doing this work on x86, you want to consider using hardware
instruction breakpoints instead of software breakpoints if you are
moving pages of the kernel around, because a software breakpoint works
with instruction replacement and pages that get copied over pages will
erase the breakpoints. In gdb you can use "hbreak" instead of "break"
for a hardware instruction breakpoint.
And of course. Good luck with your debugging. :-)
Cheers,
Jason.
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