linux-kernel - Re: [RFC][PATCH 1/6] x86: Annotate _THIS_IP

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Message-ID: <20211124181814.2ahj7ppt6kewcjmb@treble>
Date:   Wed, 24 Nov 2021 10:18:14 -0800
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Mark Rutland <mark.rutland@....com>, x86@...nel.org,
        joao@...rdrivepizza.com, hjl.tools@...il.com,
        andrew.cooper3@...rix.com, linux-kernel@...r.kernel.org,
        ndesaulniers@...gle.com, keescook@...omium.org,
        samitolvanen@...gle.com
Subject: Re: [RFC][PATCH 1/6] x86: Annotate _THIS_IP_

On Tue, Nov 23, 2021 at 03:14:45PM +0100, Peter Zijlstra wrote:
> On Tue, Nov 23, 2021 at 01:53:49PM +0000, Mark Rutland wrote:
> > On Mon, Nov 22, 2021 at 06:03:02PM +0100, Peter Zijlstra wrote:
> > > In order to find _THIS_IP_ code references in objtool, annotate them.
> > 
> > Just to check my understanding, IIUC this is because in later patches
> > you'll look at text relocations to spot missing ENDBRs, and when doing
> > so you need to filter out _THIS_IP_ instances, since those don't need an
> > ENDBR. Is that right?
> > 
> > Just checking I haven't missed some other concern that might apply to
> > arm64's BTI (Branch Target Identifier), which are analagous to ENDBR.
> 
> Correct; since _THIS_IP_ is never used for control flow (afaik, let's
> hope to $deity etc..) we can ignore any relocation resulting from it
> (lots!).

This would all be good context to add to the commit message.

-- 
Josh