Re: [PATCH v2] arm: kgdb: Fix registers on sleeping tasks

From: Stephen Boyd
Date: Wed Aug 26 2015 - 18:12:31 EST

On 08/26, Douglas Anderson wrote:
> From: Doug Anderson <dianders@xxxxxxxxxxxx>
> Dumping registers from other sleeping tasks in KGDB was totally
> failing for me. All registers were reported as 0 in many cases.
> The code was using task_pt_regs(task) to try to get other thread
> registers. This doesn't appear to be the right place to look. From
> my tests, I saw non-zero values in this structure when we were looking
> at a kernel thread that had a userspace task associated with it, but
> it contained the register values from the userspace task. So even in
> the cases where registers weren't reported as 0 we were still not
> showing the right thing.
> Instead of using task_pt_regs(task) let's use task_thread_info(task).
> This is the same place that is referred to when doing a dump of all
> sleeping task stacks (kdb_show_stack() -> show_stack() ->
> dump_backtrace() -> unwind_backtrace() -> thread_saved_sp()).
> As further evidence that this is the right thing to do, you can find
> the following comment in "gdbstub.c" right before it calls
> sleeping_thread_to_gdb_regs():
> Pull stuff saved during switch_to; nothing else is accessible (or
> even particularly relevant). This should be enough for a stack
> trace.
> ...and if you look at switch_to() it only saves r4-r11, sp and lr.
> Those are the same registers that I'm getting out of the
> task_thread_info().
> With this change you can use "info thread" to see all tasks in the
> kernel and you can switch to other tasks and examine them in gdb.
> Signed-off-by: Doug Anderson <dianders@xxxxxxxxxxxx>
> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
> ---

Works for me.

Tested-by: Stephen Boyd <sboyd@xxxxxxxxxxxxx>

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