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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