linux-kernel - Re: [PATCH v6 10/10] x86/retpoline: Exclude objtool with retpoline

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Message-ID: <1515407640.7317.27.camel@amazon.co.uk>
Date:   Mon, 8 Jan 2018 10:34:00 +0000
From:   "Woodhouse, David" <dwmw@...zon.co.uk>
To:     Thomas Gleixner <tglx@...utronix.de>, Amit Shah <aams@...zon.de>
CC:     Andi Kleen <ak@...ux.intel.com>, Paul Turner <pjt@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "Dave Hansen" <dave.hansen@...el.com>,
        Kees Cook <keescook@...gle.com>,
        "Rik van Riel" <riel@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Andy Lutomirski" <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>, <gnomes@...rguk.ukuu.org.uk>
Subject: Re: [PATCH v6 10/10] x86/retpoline: Exclude objtool with retpoline

On Mon, 2018-01-08 at 11:25 +0100, Thomas Gleixner wrote:
> On Sun, 7 Jan 2018, David Woodhouse wrote:
> 
> Cc+ Josh Poimboeuf <jpoimboe@...hat.com>
> 
> Sigh....
> 
> > From: Andi Kleen <ak@...ux.intel.com>
> > 
> > objtool's assembler nanny currently cannot deal with the code generated
> > by the retpoline compiler and throws hundreds of warnings, mostly
> > because it sees calls that don't have a symbolic target.
> > 
> > Exclude all the options that rely on objtool when RETPOLINE is active.
> > 
> > This mainly means that we use the frame pointer unwinder and livepatch
> > is not supported.
> > 
> > Eventually objtool can be fixed to handle this.

I believe Josh is on vacation and I've asked Amit to take a look at
this, at least as far as ensuring that it doesn't actually disable
kpatch.
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