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

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Message-ID: <20171116213702.GA10616@samitolvanen.mtv.corp.google.com>
Date:   Thu, 16 Nov 2017 13:37:03 -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 Thu, Nov 16, 2017 at 04:34:03PM +0000, Ard Biesheuvel wrote:
> You still have not explained to us how GOLD avoids the erratum.

Sorry, I didn't realize you were asking that. If gold spots erratum
sequences, looks like it creates stubs to break them up:

  https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=gold/aarch64.cc#l8396

It also attempts to optimize the code by replacing adrps in these
sequences with adr where possible, but otherwise doesn't appear to
touch them:

  https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=gold/aarch64.cc#l2053

Sami