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

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Message-ID: <YDZoEehURLLI/lWq@hirez.programming.kicks-ass.net>
Date:   Wed, 24 Feb 2021 15:52:01 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
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 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.