linux-kernel - Re: [PATCH 07/24] arm64: ilp32: add documentation on the ILP32 ABI for ARM64

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Message-ID: <20180524121524.GA3873@yury-thinkpad>
Date:   Thu, 24 May 2018 15:15:24 +0300
From:   Yury Norov <ynorov@...iumnetworks.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-api@...r.kernel.org, Adam Borowski <kilobyte@...band.pl>,
        Alexander Graf <agraf@...e.de>,
        Alexey Klimov <klimov.linux@...il.com>,
        Andreas Schwab <schwab@...e.de>,
        Andrew Pinski <pinskia@...il.com>,
        Bamvor Zhangjian <bamv2005@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Christoph Muellner <christoph.muellner@...obroma-systems.com>,
        Dave Martin <Dave.Martin@....com>,
        "David S . Miller" <davem@...emloft.net>,
        Florian Weimer <fweimer@...hat.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        James Hogan <james.hogan@...tec.com>,
        James Morse <james.morse@....com>,
        Joseph Myers <joseph@...esourcery.com>,
        Lin Yongting <linyongting@...wei.com>,
        Manuel Montezelo <manuel.montezelo@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Nathan_Lynch <Nathan_Lynch@...tor.com>,
        Philipp Tomsich <philipp.tomsich@...obroma-systems.com>,
        Prasun Kapoor <Prasun.Kapoor@...iumnetworks.com>,
        Ramana Radhakrishnan <ramana.gcc@...glemail.com>,
        Steve Ellcey <sellcey@...iumnetworks.com>,
        Szabolcs Nagy <szabolcs.nagy@....com>
Subject: Re: [PATCH 07/24] arm64: ilp32: add documentation on the ILP32 ABI
 for ARM64

Hi Pavel,

On Wed, May 23, 2018 at 04:06:20PM +0200, Pavel Machek wrote:
> On Wed 2018-05-16 11:18:52, Yury Norov wrote:
> > Based on Andrew Pinski's patch-series.
> > 
> > Signed-off-by: Yury Norov <ynorov@...iumnetworks.com>
> 
> So Andrew's signoff should be here?

Yes it should, but it lost since v4. I'll restore it.
 
> > ---
> >  Documentation/arm64/ilp32.txt | 45 +++++++++++++++++++++++++++++++++++
> >  1 file changed, 45 insertions(+)
> >  create mode 100644 Documentation/arm64/ilp32.txt
> > 
> > diff --git a/Documentation/arm64/ilp32.txt b/Documentation/arm64/ilp32.txt
> > new file mode 100644
> > index 000000000000..d0fd5109c4b2
> > --- /dev/null
> > +++ b/Documentation/arm64/ilp32.txt
> > @@ -0,0 +1,45 @@
> > +ILP32 AARCH64 SYSCALL ABI
> > +=========================
> > +
> > +This document describes the ILP32 syscall ABI and where it differs
> > +from the generic compat linux syscall interface.
> 
> I was hoping to learn what ILP32 is / what is it good for, but no,
> this does not tell me... it would be good to do a short explanation
> here, and maybe reference it from cover letter of the series...
> 								Pavel

ILP32 is ABI acronym that means "Integers, Longs and Pointers are 32-bit".
And LP64 means "Longs and Pointers are 64-bit".

There's AN490 - "ILP32 for AArch64 Whitepaper" from ARM which covers
the topic:
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dai0490a/ar01s01.html

And some talks:
http://connect.linaro.org/resource/bkk16/bkk16-305b/

Briefly, ILP32 is 32-bit ABI that works with AARCH64 instruction set. It looks
better in some performance tests, and is useful for compatibility with 32-bit
legacy code.

If you're more familiar with x86 terminology, in ARM world LP64 corresponds
to x86_64, AARCH32_EL0 corresponds to x86_32, and ILP32 corresponds to x32
ABI.

I'll add link to AN490 in next submission.

Yury

> -- 
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html