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Date: Mon, 17 Nov 2014 13:21:03 +0100
From: Arnd Bergmann <arnd@...db.de>
To: linux-arm-kernel@...ts.infradead.org
Cc: Catalin Marinas <catalin.marinas@....com>, Russell King - ARM Linux <linux@....linux.org.uk>, Szabolcs Nagy <nsz@...t70.net>, Rich Felker <dalias@...c.org>, Kees Cook <keescook@...omium.org>, "musl@...ts.openwall.com" <musl@...ts.openwall.com>, Andy Lutomirski <luto@...capital.net>
Subject: Re: ARM atomics overhaul for musl
On Monday 17 November 2014 11:48:33 Catalin Marinas wrote:
> On Sun, Nov 16, 2014 at 04:33:56PM +0000, Russell King - ARM Linux wrote:
> > On Sun, Nov 16, 2014 at 12:56:56AM -0500, Rich Felker wrote:
> > > Aside from that, the only case among the above that's "right" already
> > > is v7+. Hard-coding the mcr-based barrier on v6 is wrong because it's
> >
> > I don't think it's wrong at all. The instruction isn't going away from
> > ARMv7, because ARMv7 deprecates it, but it _still_ has to be implemented
> > by a CPU conforming to ARMv7. As ARMv7 is going to be the last 32-bit
> > ARM architecture, we aren't going to see the MCR instruction disappearing
> > on 32-bit CPUs.
>
> You are wrong here. ARMv8-A supports 32-bit at all levels. ARMv8-R is
> 32-bit only (and it even has an MMU at EL1). And there is a slight
> chance that we may even see 32-bit only ARMv8-A implementations (I'm not
> really giving a hint and I'm not aware of any but I don't see anything
> preventing this, it's all marketing driven).
FWIW, both Samsung EXYNOS and Qualcomm Snapdragon SoCs based on Cortex-A53
have been shipped in 32-bit only devices.
Arnd
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