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

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Date:   Tue, 3 Jul 2018 10:38:53 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        the arch/x86 maintainers <x86@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Linux Kernel Mailing List <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>,
        "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>,
        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 <linux-arm-kernel@...ts.infradead.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v9 0/6] add support for relative references in special
 sections


* Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:

> On 27 June 2018 at 17:15, Will Deacon <will.deacon@....com> wrote:
> > 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 all.
> 
> Thomas, Ingo,
> 
> Except for the below tweak against patch #3 for powerpc, which may
> apparently get confused by an input section called .discard without
> any suffixes, this series is good to go, but requires your ack to
> proceed, so I would like to ask you to share your comments and/or
> objections. Also, any suggestions or recommendations regarding the
> route these patches should take are highly appreciated.

LGTM:

Acked-by: Ingo Molnar <mingo@...nel.org>

Regarding route - I suspect -mm would be good, or any other tree that does a lot 
of cross-arch testing?

Thanks,

	Ingo