linux-kernel - Re: Can we drop upstream Linux x32 support?

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Date:   Wed, 12 Dec 2018 09:12:34 +0000
From:   Steven Newbury <steve@...wbury.org.uk>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        macro@...ux-mips.org, tg@...bsd.de, luto@...nel.org, arnd@...db.de,
        dalias@...c.org, s@...oud.org, catalin.marinas@....com,
        fweimer@...hat.com, glaubitz@...sik.fu-berlin.de,
        christian.brauner@...onical.com, hjl.tools@...il.com, hpa@...or.com
Subject: Re: Can we drop upstream Linux x32 support?

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First off I'd like to request: Please don't break my userspace!

I have a number of systems running with x32-abi as native.  They work
well, I've no want or desire to upgrade their memory or CPUs to make
keep them working as well as they do now.  Let alone the hassle of
having to redeploy with a completely different ABI.

I've been working on getting as much userspace as I can working with
x32 since it first became somewhat usable, I've sent patches upstream
and pushed to encourage projects to write portable code.  Sometimes
that has meant just little tweaks to build systems, or sometimes
disabling asm where I consider it isn't worth the effort of making it
work.  For other projects I've converted the asm or even in some cases
got the JIT working, mozjs17 for example.

So I'm both a user and a developer.

Breaking support for x32 would be really bad for me, but if I'm the
only one using it I suppose I can't really justify it being kept on
that basis.  I know CERN has sucessfully experimented with it over the
years though, so I wouldn't be surprised if there are other users
hiding out there.

I can't help but wonder if it wouldn't make more sense to drop x86
support from long mode than x32.  AMD64 x86 support was always intended
 as a compatibility feature, I very much doubt there are more people
out there using an x86 native userspace on a 64 bit kernel than there
are native x32 users.  x86 support could be implemented via KVM and/or
qemu-user.  There is no reason to keep the extra complexity in the
kernel for what is effectively an emulation layer anyway.
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