From mboxrd@z Thu Jan 1 00:00:00 1970 From: catalin.marinas@arm.com (Catalin Marinas) Date: Mon, 7 Jul 2014 15:52:08 +0100 Subject: Android and compatibility with deprecated armv7 instructions In-Reply-To: References: <20140701234800.GA23577@sirena.org.uk> <4473002.jGohFvPsvi@wuerfel> <7B049AD4-78F8-4494-A2CB-57DD346107DA@arm.com> <201407061739.22152.arnd@arndb.de> Message-ID: <20140707145208.GC32578@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Jul 07, 2014 at 01:59:54PM +0000, Janne Grunau wrote: > Arnd Bergmann arndb.de> writes: > > but I don't see how we could emulate IT without anything > > short of a full interpretation of user instructions from the kernel. > > Avoiding deprecated forms of IT would be harder. It's used more often in > libav (~50 times) Is this explicitly written IT instructions or in generated code (gas, gcc)? > so it should be only disabled if it's emulated or not > available using an explicit HWCAP. Not using Thumb for those functions would > be another option for libav. Again this doesn't fix existing binaries and it > doesn't fix compiled code. As I said, I don't see this going away (easily). I've heard the toolchain guys adding warnings but they don't help unless you rebuild your code. Given the amount of IT instructions, I don't even propose adding emulation/warnings to the kernel for the time being (that would be step 1 in my "instruction deprecation" proposal, we have to think about it; some trapping would be handy to to assess the impact but still defaulting to native). -- Catalin