linux-kernel - Re: [PATCH v2 08/18] arm64: don't disable ADR_PREL_PG_HI21* with ARM64_ERRATUM

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Message-ID: <20171117184955.GA39391@samitolvanen.mtv.corp.google.com>
Date:   Fri, 17 Nov 2017 10:49:55 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        linux-kbuild@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Yury Norov <ynorov@...iumnetworks.com>,
        Alex Matveev <alxmtvv@...il.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>
Subject: Re: [PATCH v2 08/18] arm64: don't disable ADR_PREL_PG_HI21* with
 ARM64_ERRATUM_843419

On Fri, Nov 17, 2017 at 09:54:48AM +0000, Ard Biesheuvel wrote:
> OK, so all IR objects are converted into a single .o file
> encapsulating the module image. Does this give the same benefits as
> LTO linking IR objects to a fully linked executable?

Yes, it does.

> Even if it does, partial linking is not something the toolchain
> people are usually crazy about, so it would be nice to have some
> confirmation that this is a usage model that is fully supported.

I confirmed with our LLVM developers that while this is less common,
it's fully supported.

I will also drop this patch in v3 as passing code model to LLVMgold
fixes the issue with LTO.

Sami