linux-kernel - Re: [PATCH v4 00/24] ILP32 for ARM64

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Date:	Wed, 15 Apr 2015 00:28:09 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Andreas Kraschitzer <andreas.kraschitzer@...obroma-systems.com>,
	Benedikt Huber <benedikt.huber@...obroma-systems.com>,
	"Pinski, Andrew" <Andrew.Pinski@...iumnetworks.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Pinski <apinski@...ium.com>,
	Kumar Sankaran <ksankaran@....com>,
	"Dr. Philipp Tomsich" <philipp.tomsich@...obroma-systems.com>,
	Christoph Muellner <christoph.muellner@...obroma-systems.com>
Subject: Re: [PATCH v4 00/24] ILP32 for ARM64

On Tuesday 14 April 2015 16:00:34 Catalin Marinas wrote:
> On Tue, Apr 14, 2015 at 04:07:36PM +0200, Arnd Bergmann wrote:
> > For completeness, there is yet another option, which would be to use the
> > exact system call table from arm64 and do all the emulation in user space
> > rather than the kernel. This would however be the least compatible with
> > existing source code, so you probably don't want to do that.
> 
> It would be great if this worked but I think we looked at it before and
> it seems nice until you hit the futex stuff and robust lists (I don't
> fully remember the details). Some of the structures (siginfo) would no
> longer be POSIX compliant and some of them aren't only accessed via libc
> to be able to create shadow copies.

Well, that may or may not be acceptable. Aarch64-ilp32 mode is a hack to
enable a very special class of applications, it's not like anyone would
want to run a full system for this and need POSIX compliance.

We could definitely be pragmatic and do whatever helps get the job
done. That said, it diverges further from what legacy 32-bit applications
expect to see, so this approach will likely make an application port harder,
not easier.

	Arnd
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