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Date: Sat, 28 Jun 2014 00:40:17 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: Russell King - ARM Linux <linux@....linux.org.uk>
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
* 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+
and i think the kernel can avoid the barriers on non-smp systems making
kuser helpers possibly preferable even if TLS HWCAP flag is set
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