linux-kernel - Re: objtool segfault with ORC unwinder enabled

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Date:   Wed, 3 Jan 2018 15:14:01 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Markus <M4rkusXXL@....de>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: objtool segfault with ORC unwinder enabled

On Wed, Jan 03, 2018 at 01:22:07PM +0100, Markus wrote:
> On Wed, Jan 03, 2018 at 12:19:41 CET Greg Kroah-Hartman wrote:
> > On Wed, Jan 03, 2018 at 11:49:08AM +0100, Markus wrote:
> > > Hello!
> > > 
> > > ORC unwinder is enabled in stable for wider testing but still at least one
> > > bug is open:
> > > https://bugzilla.kernel.org/show_bug.cgi?id=197035
> > 
> > Random web links on mailing lists don't help much, please put the
> > information here in the email.
> 
> Its not a random web link. Its the official kernel.org bugtracker. But nobody 
> seems to be looking at it.

Not all subsystems use bugzilla.kernel.org, sorry.  Email is the
preferred way for almost all subsystems.

> > > objtool will segfault because a NULL pointer is dereferenced.
> > 
> > And how are you reproducing this?
> 
> Just building the kernel with ORC enabled.
> (At least for me. Using framepointers compiles, enabling ORC again breaks it.)
> gcc 6.4.0 (In bug report others were tested as well.)
> elfutils 0.170
> What else may be interesting?

Have you tried gcc 7?

What distro is this?  Hopefully not hardened Gentoo?  :)

> > > Is a NULL pointer sym valid?
> > > If a NULL pointer is invalid, it has to be checked why it is sometimes
> > > NULL.
> > What .config is triggering this problem?
> See attachment.
> 
> > And does this show up on 4.14.11, and 4.15-rc6?
> Both: yes.
> 
> /tools/objtool/objtool orc generate --no-fp "arch/x86/kernel/irq.o"
> 
> => segfault.

Ugh, I can't duplicate here :(

Josh, any ideas?

greg k-h