linux-kernel - Re: [PATCH v9 0/6] add support for relative references in special sections

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Date:   Wed, 27 Jun 2018 16:15:11 +0100
From:   Will Deacon <will.deacon@....com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        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>,
        Petr Mladek <pmladek@...e.com>, Ingo Molnar <mingo@...hat.com>,
        James Morris <jmorris@...ei.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nicolas Pitre <nico@...aro.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jessica Yu <jeyu@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: Re: [PATCH v9 0/6] add support for relative references in special
 sections

Hi Ard,

On Tue, Jun 26, 2018 at 08:27:55PM +0200, Ard Biesheuvel wrote:
> 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)
> 
> Patch #3 was sent out before as a single patch. This series supersedes
> the previous submission. This version makes relative ksymtab entries
> dependent on the new Kconfig symbol HAVE_ARCH_PREL32_RELOCATIONS rather
> than trying to infer from kbuild test robot replies for which architectures
> it should be blacklisted.
> 
> Patch #1 introduces the new Kconfig symbol HAVE_ARCH_PREL32_RELOCATIONS,
> and sets it for the main architectures that are expected to benefit the
> most from this feature, i.e., 64-bit architectures or ones that use
> runtime relocations.
> 
> Patch #2 add support for #define'ing __DISABLE_EXPORTS to get rid of
> ksymtab/kcrctab sections in decompressor and EFI stub objects when
> rebuilding existing C files to run in a different context.

I had a small question on patch 3, but it's really for my understanding.
So, for patches 1-3:

Reviewed-by: Will Deacon <will.deacon@....com>

Thanks,

Will