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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        linux-kernel@vger.kernel.org
Cc:     Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Kees Cook <keescook@chromium.org>,
        Will Deacon <will.deacon@arm.com>,
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        Thomas Gleixner <tglx@linutronix.de>,
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        Bjorn Helgaas <bhelgaas@google.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Russell King <linux@armlinux.org.uk>,
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        Catalin Marinas <catalin.marinas@arm.com>,
        Petr Mladek <pmladek@suse.com>, Ingo Molnar <mingo@redhat.com>,
        James Morris <jmorris@namei.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nicolas Pitre <nico@linaro.org>,
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        Jessica Yu <jeyu@kernel.org>,
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        linuxppc-dev@lists.ozlabs.org, x86@kernel.org
Subject: Re: [PATCH v9 0/6] add support for relative references in special sections
In-Reply-To: <20180626182802.19932-1-ard.biesheuvel@linaro.org>
References: <20180626182802.19932-1-ard.biesheuvel@linaro.org>
Date:   Wed, 27 Jun 2018 15:33:44 +1000
Message-ID: <87r2ks6bev.fsf@concordia.ellerman.id.au>
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Sender: linux-kernel-owner@vger.kernel.org
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Ard Biesheuvel <ard.biesheuvel@linaro.org> writes:
> This adds support for emitting special sections such as initcall arrays,
> PCI fixups and tracepoints as relative references rather than absolute
> references. This reduces the size by 50% on 64-bit architectures, but
> more importantly, it removes the need for carrying relocation metadata
> for these sections in relocatable kernels (e.g., for KASLR) that needs
> to be fixed up at boot time. On arm64, this reduces the vmlinux footprint
> of such a reference by 8x (8 byte absolute reference + 24 byte RELA entry
> vs 4 byte relative reference)
...
>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>

This seems to be working on powerpc.

It boots on a couple of machines with no obvious badness.

And there's some size reduction with a random config I had lying around:

  Total: Before=14820494, After=14673313, chg -0.99%


It can get some more testing once it's in linux-next as far as I'm
concerned.

  Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)

cheers