linux-kernel - Re: [PATCH] arm64: prevent regressions in compressed kernel image size when upgrading to binutils 2.27

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Message-ID: <CAFrQcG_VRr40JG3GeS3nYqQW0kQpkiMk-tOLg8zR064cmEwTZQ@mail.gmail.com>
Date:   Thu, 26 Oct 2017 14:51:51 -0700
From:   Siqi Lin <siqilin@...gle.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Kees Cook <keescook@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Jiri Kosina <jikos@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Will Deacon <will.deacon@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>, Wei Wang <wvw@...gle.com>,
        Gopinath Elanchezhian <gelanchezhian@...gle.com>,
        spentyala@...gle.com, Rahul Chaudhry <rahulchaudhry@...gle.com>,
        Stephen Hines <srhines@...gle.com>
Subject: Re: [PATCH] arm64: prevent regressions in compressed kernel image
 size when upgrading to binutils 2.27

On Thu, Oct 26, 2017 at 2:23 PM, Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Thu, Oct 26, 2017 at 2:17 PM, Siqi Lin <siqilin@...gle.com> wrote:
> > I'm OK with sticking with the <2.27 binutils behavior. The gzip data is:
>
> That's what this patch does; goes back to the <2.27 behavior for 2.27+.
>
> > binutils 2.25:
> > Image 41467904
> > Image.gz 13395151
> > binutils 2.27:
> > Image 41467392
> > Image.gz 14114953
> >
> > gzipped kernel increased by 0.69 MiB.
>
> That's without this patch applied?  With it applied, what are the
> stats (for gzip)?
>

binutils 2.27 with this patch (with --no-apply-dynamic-relocs):
Image 41535488
Image.gz 13404067

binutils 2.27 without this patch (without --no-apply-dynamic-relocs):
Image 41535488
Image.gz 14125516

The 2.27 gzipped size with this patch is about the same as 2.25.

> > The one special case I see is !CONFIG_RELOCATABLE and compression is
> > used, where there's a tradeoff between compressed image size and the
> > benefit of dynamic relocs.
>
> if !CONFIG_RELOCATABLE, then this patch (well v2 which will use
> CONFIG_RELOCATABLE rather than CONFIG_RANDOMIZE_BASE) doesn't do
> anything.