linux-kernel - Re: [PATCH v8 03/12] x86/retpoline: Add initial retpoline support

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Date:   Sun, 14 Jan 2018 09:53:45 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     David Woodhouse <dwmw@...zon.co.uk>,
        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>, tglx@...utronix.de,
        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,
        x86@...nel.org, thomas.lendacky@....com
Subject: Re: [PATCH v8 03/12] x86/retpoline: Add initial retpoline support

On Sun, Jan 14, 2018 at 04:02:19PM +0100, Borislav Petkov wrote:
> On Thu, Jan 11, 2018 at 09:46:25PM +0000, David Woodhouse wrote:
> > +/*
> > + * This should be used immediately before a retpoline alternative.  It tells
> > + * objtool where the retpolines are so that it can make sense of the control
> > + * flow by just reading the original instruction(s) and ignoring the
> > + * alternatives.
> > + */
> > +.macro ANNOTATE_NOSPEC_ALTERNATIVE
> > +	.Lannotate_\@:
> > +	.pushsection .discard.nospec
> > +	.long .Lannotate_\@ - .
> > +	.popsection
> > +.endm
> 
> Hey Josh, what happened to parsing only the retpoline-related
> .altinstructions sections with the X86_FEATURE bits? Or is this
> annotation used for something more additionally?

Yeah, that idea came after this patch was already written.  I haven't
implemented it yet.

-- 
Josh