Android and compatibility with deprecated armv7 instructions

[Grant Likely]

On Wed, Jul 2, 2014 at 6:01 PM, Will Deacon <will.deacon at arm.com> wrote:
> On Wed, Jul 02, 2014 at 05:39:23PM +0100, Mark Brown wrote:
>> On Wed, Jul 02, 2014 at 11:01:33AM +0100, Will Deacon wrote:
>>
>> >   (1) The hardware doesn't have the instruction at all. If we start
>> >       emulating it, then we'll always have to emulate it and it doesn't
>> >       encourage software migration.
>>
>> That's what the logging other architectures did in similar situations
>> was intended to help address - even if people don't care about the
>> performance impact having loud complaints in the logs tends to cause
>> some useful subset of users to report it as a problem.
>
> I don't think logging something to dmesg is going to make a blind bit of
> difference on an Android device. Maybe we could get SWP emulation to request
> access to the users contacts and send everybody a text message each time
> they issue the instruction?
>
> Seriously though, nothing causes loud complaints like a SIGILL. This thread
> is evidence of that.

I think that looks at the problem entirely the wrong way around. We
don't break userspace. That's been a rule for a very long time.
Android is not the embedded world where we could get away with a whole
lot. There is a *freaking huge* installed base of applications.
Breaking them is not an option, and I think Colin's question makes it
clear that Android is going make sure that doesn't happen regardless
of what the mainline kernel does... and they are right to do so.

g.