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Message-ID: <20180516152913.GY1392@brightrain.aerifal.cx>
Date: Wed, 16 May 2018 11:29:13 -0400
From: Rich Felker <dalias@...c.org>
To: Dave Martin <Dave.Martin@....com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
Richard Henderson <rth@...ddle.net>,
Ivan Kokshaysky <ink@...assic.park.msu.ru>,
Matt Turner <mattst88@...il.com>,
Russell King <linux@...linux.org.uk>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
Tony Luck <tony.luck@...el.com>,
Fenghua Yu <fenghua.yu@...el.com>,
Michal Simek <monstr@...str.eu>,
Ralf Baechle <ralf@...ux-mips.org>,
James Hogan <jhogan@...nel.org>,
Greentime Hu <green.hu@...il.com>,
Vincent Chen <deanbo422@...il.com>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
Michael Ellerman <mpe@...erman.id.au>,
Palmer Dabbelt <palmer@...ive.com>,
Albert Ou <albert@...ive.com>,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Yoshinori Sato <ysato@...rs.sourceforge.jp>,
"David S. Miller" <davem@...emloft.net>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, Chris Zankel <chris@...kel.net>,
Max Filippov <jcmvbkbc@...il.com>
Subject: Re: [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note
reservations
On Wed, May 16, 2018 at 03:20:47PM +0100, Dave Martin wrote:
> There are constraints on defining AT_* auxvec tags that are not
> obvious to the casual maintainer of either the global
> <uapi/linux/auxvec.h> or the arch-specific headers. This is likely
> to lead to mistakes. (I certainly fell foul of it...)
>
> For the benefit of future maintainers, this patch collects the
> relevant information in one place, documenting how the namespace
> needs to be managed, and noting all the values currently in use.
>
> Maintaining a global list may result in some merge conflicts, but
> AT_* values are not added frequently. I'm open to suggestions on
> the best approach.
>
> I also assume that values 38 and 39 may have been used for
> historical purposes, such as an architecture that is no longer
> supported. If they have definitely never been used for anything,
> they could be removed from the "reserved" list.
On the userspace side (elf.h) all the AT_* constants are in one file.
Why don't we just do the same here and eliminate the
arch/*/include/uapi/asm/auxvec.h files and likewise the need to
manually maintain consistency of the comments about reservations?
If there are reasons not to do that, I'm not opposed to this patch
as-is.
Rich
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