linux-kernel - Re: [RFC] Objtool toolchain proposal: -fannotate-{jump-table,noreturn}

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Message-ID: <Yx3+GpHakZZYLM1N@hirez.programming.kicks-ass.net>
Date:   Sun, 11 Sep 2022 17:26:18 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     linux-toolchains@...r.kernel.org,
        Indu Bhagat <indu.bhagat@...cle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, "Jose E. Marchesi" <jemarch@....org>,
        Miroslav Benes <mbenes@...e.cz>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>, x86@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        live-patching@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Ard Biesheuvel <ardb@...nel.org>,
        Chen Zhongjin <chenzhongjin@...wei.com>,
        Sathvika Vasireddy <sv@...ux.ibm.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [RFC] Objtool toolchain proposal:
 -fannotate-{jump-table,noreturn}

On Fri, Sep 09, 2022 at 11:07:04AM -0700, Josh Poimboeuf wrote:
> Alternatives
> ------------
> 
> Another idea which has been floated in the past is for objtool to read
> DWARF (or .eh_frame) to help it figure out the control flow.  That
> hasn't been tried yet, but would be considerably more difficult and
> fragile IMO.

I though Ard played around with that a bit on ARM64. And yes, given that
most toolchains consider DWARF itself best-effort, I'm not holding my
breath there.

On top of that, building a kernel with DWARFs on is just so much
slower..