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

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Message-ID: <20190716230336.y7nk24ybbwguio2s@treble>
Date:   Tue, 16 Jul 2019 18:03:36 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Nick Desaulniers <ndesaulniers@...gle.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 Wed, Jul 17, 2019 at 12:05:14AM +0200, Arnd Bergmann wrote:
> 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.

Right.

-- 
Josh