linux-kernel - Re: [PATCH v5 1/8] arch: enable relative relocations for arm64, power, x86, s390 and x86

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Date:   Mon, 25 Dec 2017 21:09:48 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Arnd Bergmann <arnd@...db.de>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Kees Cook <keescook@...omium.org>,
        Will Deacon <will.deacon@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Garnier <thgarnie@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Russell King <linux@...linux.org.uk>,
        Paul Mackerras <paulus@...ba.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Petr Mladek <pmladek@...e.com>, Ingo Molnar <mingo@...hat.com>,
        James Morris <james.l.morris@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nicolas Pitre <nico@...aro.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jessica Yu <jeyu@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-s390@...r.kernel.org, sparclinux@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH v5 1/8] arch: enable relative relocations for arm64,
 power, x86, s390 and x86

On 25 December 2017 at 21:05, Sam Ravnborg <sam@...nborg.org> wrote:
> Hi Ard.
>
> On Mon, Dec 25, 2017 at 08:54:33PM +0000, Ard Biesheuvel wrote:
>> Before updating certain subsystems to use place relative 32-bit
>> relocations in special sections, to save space  and reduce the
>> number of absolute relocations that need to be processed at runtime
>> by relocatable kernels, introduce the Kconfig symbol and define it
>> for some architectures that should be able to support and benefit
>> from it.
>>
>> Cc: Catalin Marinas <catalin.marinas@....com>
>> Cc: Will Deacon <will.deacon@....com>
>> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
>> Cc: Paul Mackerras <paulus@...ba.org>
>> Cc: Michael Ellerman <mpe@...erman.id.au>
>> Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
>> Cc: Heiko Carstens <heiko.carstens@...ibm.com>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: "H. Peter Anvin" <hpa@...or.com>
>> Cc: x86@...nel.org
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>> ---
>>  arch/Kconfig                    | 10 ++++++++++
>>  arch/arm64/Kconfig              |  1 +
>
>>  arch/arm64/kernel/vmlinux.lds.S |  2 +-
> The change to arch/arm64/kernel/vmlinux.lds.S is
> not justified in the changelog.
> Did you add it by mistake?
>

No. The PREL32 support adds a __ADDRESSABLE() macro that emits code
into .discard.text, and on arm64, the EFI object sections get a .init
prefix so we need to discard .init.discard.* explicitly as well.

I will add this as a note.

Thanks,
Ard.