linux-kernel - Re: [PATCH 2/3] objtool: Ignore retpoline alternatives

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Message-ID: <20180111173744.2iysfjky7hbjozqf@treble>
Date:   Thu, 11 Jan 2018 11:37:44 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andi Kleen <ak@...ux.intel.com>, Paul Turner <pjt@...gle.com>,
        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>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>,
        One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Subject: Re: [PATCH 2/3] objtool: Ignore retpoline alternatives

On Thu, Jan 11, 2018 at 09:29:48AM -0800, Linus Torvalds wrote:
> That, btw, is also why it's pointless to make the small numbers
> "bigger". Using "1122" as a label is actively worse than just using
> "1".
> 
> You shouldn't try to fool yourself and think that your number is
> "unique". It doesn't need to be. A label needs to be unique within one
> use, and the use just tells _which_ of the non-unique numbers you use.
> 
> And yes, you could even re-use the number within one macro or inline
> asm. But that's just confusing. Make the number unique for the
> particular macro or inline use.

What if the macro is used by another macro which needs to jump across
it?  If the labels conflict then the outer macro will accidentally jump
to the inner macro.

-- 
Josh