linux-kernel - Re: [RFC][PATCH] objtool: STAC/CLAC validation

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Message-ID: <20190223083942.GF32477@hirez.programming.kicks-ass.net>
Date:   Sat, 23 Feb 2019 09:39:42 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     hpa@...or.com
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Julien Thierry <julien.thierry@....com>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...nel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        "linux-alpha@...r.kernel.org" <linux-arm-kernel@...ts.infradead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>, valentin.schneider@....com,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Denys Vlasenko <dvlasenk@...hat.com>
Subject: Re: [RFC][PATCH] objtool: STAC/CLAC validation

On Fri, Feb 22, 2019 at 03:39:48PM -0800, hpa@...or.com wrote:
> Objtool could also detect CLAC-STAC or STAC-CLAC sequences without
> memory operations and remove them; don't know how often that happens,
> but I know it *does* happen.

Objtool doesn't know about memops; that'd be a lot of work. Also,
objtool doesn't actually rewrite the text, at best it could warn about
such occurences.