linux-kernel - Re: [PATCH 2/2] x86/unwind/orc: Silence warnings caused by missing ORC data

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Message-ID: <20210224151805.zrujocamlb5pxf7m@treble>
Date:   Wed, 24 Feb 2021 09:18:05 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Ivan Babrou <ivan@...udflare.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 2/2] x86/unwind/orc: Silence warnings caused by missing
 ORC data

On Wed, Feb 24, 2021 at 03:52:01PM +0100, Peter Zijlstra wrote:
> On Fri, Feb 05, 2021 at 08:24:03AM -0600, Josh Poimboeuf wrote:
> > The ORC unwinder attempts to fall back to frame pointers when ORC data
> > is missing for a given instruction.  It sets state->error, but then
> > tries to keep going as a best-effort type of thing.  That may result in
> > further warnings if the unwinder gets lost.
> > 
> > Until we have some way to register generated code with the unwinder,
> > missing ORC will be expected, and occasionally going off the rails will
> > also be expected.  So don't warn about it.
> 
> I recently ran into another variant of missing ORC data, some files are
> simply not processed by objtool, eg. arch/x86/realmode/init.c. Would it
> make sense to have the vmlinux pass (when it isn't used to generate orc
> in the first place) also check that all code it finds has ORC data?
> 
> It's not fool proof, but it should help find files we're missing for
> some raisin.

Doesn't validate_reachable_instructions() basically already do that?

-- 
Josh