linux-kernel - Re: objtool crashes on clang output (drivers/hwmon/pmbus/adm1275.o)

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Date:   Wed, 17 Jul 2019 00:05:14 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, Jann Horn <jannh@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: objtool crashes on clang output (drivers/hwmon/pmbus/adm1275.o)

On Tue, Jul 16, 2019 at 10:24 PM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@...glegroups.com> wrote:
>
> On Fri, Jul 12, 2019 at 1:41 PM Arnd Bergmann <arnd@...db.de> wrote:
> >
> > On Fri, Jul 12, 2019 at 6:59 PM 'Nick Desaulniers' via Clang Built
> > Linux <clang-built-linux@...glegroups.com> wrote:
> > > > The issue still needs to get fixed in clang regardless.  There are other
> > > > noreturn functions in the kernel and this problem could easily pop back
> > > > up.
> > >
> > > Sure, thanks for the report.  Arnd, can you help us get a more minimal
> > > test case to understand the issue better?
> >
> > I reduced it to this testcase:
> >
> > int a, b;
> > void __reiserfs_panic(int, ...) __attribute__((noreturn));
> > void balance_internal() {
> >   if (a)
> >     __reiserfs_panic(0, "", __func__, "", 2, __func__, a);
> >   if (b)
> >     __reiserfs_panic(0, "", __func__, "", 5, __func__, a, 0);
> > }
> >
> > https://godbolt.org/z/Byfvmx
>
> Is this the same issue as Josh pointed out?  IIUC, Josh pointed to a
> jump destination that was past a `push %rbp`, and I don't see it in
> your link.  (Or, did I miss it?)

I think it can be any push. The point is that the stack is different
between the two branches leading up to the noreturn call.

      Arnd