Re: [PATCH 1/5] ARM: stacktrace: Skip frame pointer boundary check for call_with_stack()

[Li Huafei]

Hi Linus, sorry for the late reply.

On 2022/7/18 16:57, Linus Walleij wrote:
> On Tue, Jul 12, 2022 at 4:18 AM Li Huafei <lihuafei1@xxxxxxxxxx> wrote:
>
> > When using the frame pointer unwinder, it was found that the stack trace
> > output of stack_trace_save() is incomplete if the stack contains
> > call_with_stack():
> >
> >   [0x7f00002c] dump_stack_task+0x2c/0x90 [hrtimer]
> >   [0x7f0000a0] hrtimer_hander+0x10/0x18 [hrtimer]
> >   [0x801a67f0] __hrtimer_run_queues+0x1b0/0x3b4
> >   [0x801a7350] hrtimer_run_queues+0xc4/0xd8
> >   [0x801a597c] update_process_times+0x3c/0x88
> >   [0x801b5a98] tick_periodic+0x50/0xd8
> >   [0x801b5bf4] tick_handle_periodic+0x24/0x84
> >   [0x8010ffc4] twd_handler+0x38/0x48
> >   [0x8017d220] handle_percpu_devid_irq+0xa8/0x244
> >   [0x80176e9c] generic_handle_domain_irq+0x2c/0x3c
> >   [0x8052e3a8] gic_handle_irq+0x7c/0x90
> >   [0x808ab15c] generic_handle_arch_irq+0x60/0x80
> >   [0x8051191c] call_with_stack+0x1c/0x20
> >
> > For the frame pointer unwinder, unwind_frame() checks stackframe::fp by
> > stackframe::sp. Since call_with_stack() switches the SP from one stack
> > to another, stackframe::fp and stackframe: :sp will point to different
> > stacks, so we can no longer check stackframe::fp by stackframe::sp. Skip
> > checking stackframe::fp at this point to avoid this problem.
> >
> > Signed-off-by: Li Huafei <lihuafei1@xxxxxxxxxx>
> Very nice catch! Took me some time to realize what was
> going on here.

Yeah, it took me some time to discover the cause of the problem too.

> Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>

Thanks!

> Nitpick below:
>
> > +       /*
> > +        * call_with_stack() is the only place we allow SP to jump from one
> > +        * stack to another, with FP and SP pointing to different stacks,
> > +        * skipping the FP boundary check at this point.
> > +        */
> > +       if (pc >= (unsigned long)&call_with_stack &&
> > +                       pc < (unsigned long)&call_with_stack_end)
> > +               return 0;
> Can we create a local helper macro to do this, if it needs to happen
> some other time?

Hopefully this won't come up again.:(

Maybe it would be better to define a macro when this happens?


Thanks,

Huafei

> #define ARM_PC_IN_FUNCTION(pc, func) (pc >=. ...)
>
> Yours,
> Linus Walleij
> .