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Non-neon Gapps (Android 4.2) dev-discussion thread

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By tonyp, Inactive Recognized Developer on 11th March 2013, 08:11 PM
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3rd January 2015, 01:58 PM |#21  
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Originally Posted by echo_21

Hi @tonyp, I hope it's ok to revive this thread again resp. to hijack it a bit from your original intention!? Even if the origin of my following NEON related questions is founded in my lag problems with CM11 2014/11/13 build by @gucky01 I find they fit this thread much better than any other CM10.x/CM11/CM12 ROM XDA thread. Not just one but all of those ROMs are affected by the missing NEON instruction set of the Tegra 2 SOC.

  1. How can one prove wether a current ROM does not call any NEON instructions? Is it sufficient to see that there are no SIGILL entries in the logs?
  2. Let's assume a dev releases a ROM that initially does not call any NEON instructions. Is it possible that updates of Google apps introduce calls of NEON instructions making the ROM misfunctional/unusable?
  3. AFAI understood your trick to assemble non-NEON gapps is to replace shared opjects ( .so files) that call NEON instructions by their (more or less) equivalent non-NEON shared objects. Could there be Google apps or third party apps that call NEON instructions in their core binary?
    If so, our P990 will not able to run them, right? I'd like to assemble a list of apps that won't run without NEON support (is there still any list?).
  4. Do calls of NEON instructions on systems that don't support NEON always result in FCs, hot re-boots, or BSODs? Other way round: can calls of NEON instructions on systems that don't support NEON also result in lag or even heavy lag? (gmail 5.0.1 uses to take 10 seconds to start in my recently installed CM11 after the cleanest install possible; I just left the BB and system data/cal un-touched).

I am looking forward for your reply, well-knowing that you don't use the P990 as your daily driver any more for a long time now.

I wish you all a good 2015!

Hey there old friend,

of course it's okay to reuse this thread.
  1. As far as I know you'll always see a SIGILL error when a module uses neon instructions.
  2. Google apps updates could in theory include neon modules.
    This is highly unlikely, though, Google supports tons of devices and the PlayStore will ship the right updates to the right phones. Remember that the Play Services supports all devices down to 2.3.
    It can be problematic for some apps that usually didn't exist on older, non-neon devices, like the Google keyboard or some Google Speech updates.
  3. Yes, I simply used modules built for non-neon devices, wherever possible.
    Apps can use neon instructions, but not within Java - so they will ship a module.
    This module can be included in the core apk, but will/can be extracted.
    At least to my knowledge there are no other ways.
  4. I don't think that it wil cause lags - at least not without showing anything in the log.
    I'm no expert at this level, we're talking about something closely hardware related.
    NEON SIMD capabilities aren't something you usally work with - in general apps use a way higher abstraction layer and don't touch anything that close to hardware instructions.
    Whenever an app uses neon instructions it will fail as our hardware doesn't support it. It won't just "work in a bad way" and thus be laggy.

I see where you are going, but I don't think that neon is related to the lag we see on KitKat.
The most obivous reason is the shortage of RAM, the second most obvious one that we're running KitKat with libs written for ICS (and even worse, apparently from a release that was rushed by LG - even if it's funny to call a ROM that was released 10 month after the official ICS upgrade rushed).
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