Re: v4.10: kernel stack frame pointer .. has bad value (null)

From	Josh Poimboeuf <jpoimboe@redhat.com>
Newsgroups	linux.kernel
Subject	Re: v4.10: kernel stack frame pointer .. has bad value (null)
Date	2017-02-22 22:20 +0100
Message-ID	<tdMun-7Lo-29@gated-at.bofh.it> (permalink)
References	<tdqWT-l3-33@gated-at.bofh.it> <tdrSV-11G-3@gated-at.bofh.it> <tdrSV-11G-1@gated-at.bofh.it> <tdIqK-4Fw-13@gated-at.bofh.it> <tdMb0-7mE-17@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Wed, Feb 22, 2017 at 12:51:11PM -0800, H. Peter Anvin wrote:
> On 02/22/17 08:45, Josh Poimboeuf wrote:
> >>
> >> FWIW, it would be really darned nice to not have all those zeroes in a
> >> 32-bit stack frame dump.
> > 
> > Yeah, I'll fix that.
> > 
> >> Is not a zero stack frame pointer value an end of stack token?
> > 
> > There's no end of stack "token" per se, though any frame pointer value
> > outside the bounds of the stack will terminate the stack trace (and that
> > still happened here).
> > 
> 
> Well, my understanding is that at least gdb and perhaps other unwinders
> consider a zero stack frame pointer to be an indicator that the stack
> has reached its end.  That's why I'm wondering if this is possible in
> this case or if it is unlikely because of the value.

I'm not sure I follow your question.  The frame pointer was zero, and
that did cause the unwinder to stop the stack trace.  The warning was
because it ended in an unexpected place.

> > The warning is because the stack trace didn't make it all the way to the
> > "end" location of the stack (right before the syscall pt_regs location).
> > The warning is part of the effort to ensure reliable stacks.
> 
> It would be useful to get an understanding why...

Agreed...

-- 
Josh

Thread

v4.10: kernel stack frame pointer .. has bad value (null) Pavel Machek <pavel@ucw.cz> - 2017-02-21 23:20 +0100
  Re: v4.10: kernel stack frame pointer .. has bad value (null) "H. Peter Anvin" <hpa@zytor.com> - 2017-02-22 00:20 +0100
    Re: v4.10: kernel stack frame pointer .. has bad value (null) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-02-22 18:00 +0100
      Re: v4.10: kernel stack frame pointer .. has bad value (null) "H. Peter Anvin" <hpa@zytor.com> - 2017-02-22 22:00 +0100
        Re: v4.10: kernel stack frame pointer .. has bad value (null) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-02-22 22:20 +0100
  Re: v4.10: kernel stack frame pointer .. has bad value (null) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-02-22 00:20 +0100
    Re: v4.10: kernel stack frame pointer .. has bad value (null) Pavel Machek <pavel@ucw.cz> - 2017-02-22 22:10 +0100
      Re: v4.10: kernel stack frame pointer .. has bad value (null) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-02-22 22:30 +0100
        Re: v4.10: kernel stack frame pointer .. has bad value (null) Pavel Machek <pavel@ucw.cz> - 2017-02-22 23:50 +0100
          Re: v4.10: kernel stack frame pointer .. has bad value (null) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-02-23 00:10 +0100
            Re: v4.10: kernel stack frame pointer .. has bad value (null) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-02-23 00:20 +0100
              Re: v4.10: kernel stack frame pointer .. has bad value (null) Josh Poimboeuf <jpoimboe@redhat.com> - 2017-02-25 06:30 +0100

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