linux-kernel - Re: gcc-8 objtool warnings

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Date:   Wed, 23 Aug 2017 11:01:03 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: gcc-8 objtool warnings

On Wed, Aug 23, 2017 at 03:38:02PM +0200, Arnd Bergmann wrote:
> On Wed, Aug 23, 2017 at 2:48 PM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > On Wed, Aug 23, 2017 at 02:22:34PM +0200, Arnd Bergmann wrote:
> >> ...
> >>
> >> 0000000000000000 <put_cred_rcu.cold.1>:
> >>    0:   e8 00 00 00 00          callq  5 <put_cred_rcu.cold.1+0x5>
> >>                         1: R_X86_64_PC32        __sanitizer_cov_trace_pc-0x4
> >>    5:   44 8b 8b 64 ff ff ff    mov    -0x9c(%rbx),%r9d
> >>    c:   48 8b 8b 68 ff ff ff    mov    -0x98(%rbx),%rcx
> >>   13:   44 89 e2                mov    %r12d,%edx
> >>   16:   44 8b 83 60 ff ff ff    mov    -0xa0(%rbx),%r8d
> >>   1d:   4c 89 ee                mov    %r13,%rsi
> >>   20:   48 c7 c7 00 00 00 00    mov    $0x0,%rdi
> >>                         23: R_X86_64_32S        .rodata.str1.8+0x28
> >>   27:   e8 00 00 00 00          callq  2c <__kstrtab_creds_are_invalid+0x3>
> >>                         28: R_X86_64_PC32       panic-0x4
> >
> > Thanks.  Can you send me one of the .o files?
> 
> Attached here now.

Ok, looks like I'll need to add support for this new pattern (jumping to
a .cold section in .text.unlikely).

I'm also about to start work on fixing that other issue you found with
GCC's inefficient update of the stack pointer.

I really appreciate your finding all these warnings (and getting advance
GCC 8 testing).  Thanks again!

-- 
Josh