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Date:   Sat, 6 Jul 2019 10:50:01 -0500
From:   Josh Poimboeuf <jpoimboe@redhat.com>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Nick Desaulniers <ndesaulniers@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Kees Cook <keescook@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Craig Topper <craig.topper@intel.com>,
        Alexander Potapenko <glider@google.com>,
        Bill Wendling <morbo@google.com>,
        Stephen Hines <srhines@google.com>
Subject: Re: objtool warnings in prerelease clang-9
Message-ID: <20190706155001.yrfxqj7c2bmqtbid@treble>
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On Tue, Jul 02, 2019 at 11:58:27PM +0200, Thomas Gleixner wrote:
> platform-quirks.o:
> 
>         if (x86_platform.set_legacy_features)
>   74:   4c 8b 1d 00 00 00 00    mov    0x0(%rip),%r11        # 7b <x86_early_init_platform_quirks+0x7b>
>   7b:   4d 85 db                test   %r11,%r11
>   7e:   0f 85 00 00 00 00       jne    84 <x86_early_init_platform_quirks+0x84>
>                 x86_platform.set_legacy_features();
> }
>   84:   c3                      retq   
> 
> That jne jumps to __x86_indirect_thunk_r11, aka. ratpoutine.
> 
> No idea why objtool thinks that the instruction at 0x84 is not
> reachable. Josh?

That's a conditional tail call, which is something GCC never does.
Objtool doesn't understand that, so we'll need to fix it.

-- 
Josh