linux-kernel - Re: [Ksummit-discuss] (Resend) 2038 Kernel Summit Discussion Fodder

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Message-ID: <20140813091837.GA18495@arm.com>
Date:	Wed, 13 Aug 2014 10:18:37 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Josh Triplett <josh@...htriplett.org>,
	John Stultz <john.stultz@...aro.org>,
	"ksummit-discuss@...ts.linuxfoundation.org" 
	<ksummit-discuss@...ts.linuxfoundation.org>,
	"Joseph S. Myers" <joseph@...esourcery.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [Ksummit-discuss] (Resend) 2038 Kernel Summit Discussion Fodder

On Wed, Aug 13, 2014 at 02:37:11AM +0100, Andy Lutomirski wrote:
> On Tue, Aug 12, 2014 at 6:33 PM,  <josh@...htriplett.org> wrote:
> > On Tue, Aug 12, 2014 at 05:08:53PM -0700, John Stultz wrote:
> >> A more aggressive version of the previous proposal is what I’m calling the
> >> “New Virtual-Architecture” approach, basically extending the versioning
> >> control from the linker down into the kernel as well.  It would be adding a
> >> new “virtual-architecture” to the kernel, not entirely unlike how x32 is
> >> supported on x86_64 systems.  We would create entirely new ABI and
> >> architecture name in the kernel (think something like “armllt” or
> >> “i386llt”). We would preserve compatibility for legacy applications via
> >> personalities, similar mechanism as the compat_ interface used to support
> >> 32bit applications on 64bit kernels. In this case, we wouldn’t introduce
> >> new 64 bit syscalls in the kernel, as the existing interfaces would just be
> >> typed correctly for our new virtual architecture, but we would have
> >> duplicate syscall interfaces via the compat interfaces. The extra
> >> complexity would also be that we would have to support new 32bit compat
> >> environment on 64bit systems. Userspace would be completely rebuilt to
> >> support the new -llt architecture, and compatibility for legacy
> >> applications would be done via the same multiarch packaging as is done now
> >> for running 32bit applications on 64bit systems.
> >
> > I wonder: could we make this new architecture effectively use the
> > signatures of the 64-bit syscalls (similar to x32), just with a 32-bit
> > calling convention?
> 
> Doesn't x32 do the reverse?  It invokes *compat* syscalls using a
> 64-bit calling convention.

Not entirely. It uses 64-bit syscalls primarily with compat only when
sharing structures containing pointers. We are working on something
similar for arm64 (called the ILP32 ABI).

-- 
Catalin
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