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Message-ID: <20140627231224.GY32514@n2100.arm.linux.org.uk>
Date: Sat, 28 Jun 2014 00:12:24 +0100
From: Russell King - ARM Linux <linux@....linux.org.uk>
To: Szabolcs Nagy <nsz@...t70.net>
Cc: Rich Felker <dalias@...c.org>, musl@...ts.openwall.com,
Kees Cook <keescook@...omium.org>,
linux-arm-kernel@...ts.infradead.org,
Andy Lutomirski <luto@...capital.net>
Subject: Re: Re: Thread pointer changes
On Sat, Jun 28, 2014 at 12:40:17AM +0200, Szabolcs Nagy wrote:
> * Russell King - ARM Linux <linux@....linux.org.uk> [2014-06-27 23:17:44 +0100]:
> > I think you're are missing one obvious solution to this which you can do:
> > you are passed the HWCAP fields in the ELF auxinfo. This will tell you
> > if the CPU has TLS support or not. If it has TLS support, then you don't
> > need to use the kuser helpers, and you know that it is a CPU which is ARM
> > architecture v6k or later, and it has things like the CP15 barrier
> > instructions. If you want to know that the CPU supports the DMB
> > instruction rather than the CP15 barrier instruction, then you have to
> > check the uname details, or read /proc/cpuinfo (but I'd rather you
> > didn't.)
> >
>
> but cp15 barrier is deprecated on armv7+
Can you _please_ read all my replies and stop cherry picking what you
want? There's many of you, and only one of me - please do me the
effort of fully reading my replies before replying on points I've
already included.
I said just after you stopped reading the above quoted text:
"If you want to know that the CPU supports the DMB instruction rather
than the CP15 barrier instruction, then you have to check the uname
details"
That's because it's an _instruction_ _set_ _architecture_ issue, and
you can get that from uname. If uname indicates v7, then you're running
on a CPU which has deprecated the CP15 barrier operations. If it
indicates v6, then you're running on a CPU which has them but has no
DMB instruction etc. If it's earlier than v6, you have no barrier
instructions what so ever.
--
FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly
improving, and getting towards what was expected from it.
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