[iOS] arm64 devices crash on ff_hscale_8_to_15_neon function with EXC_BAD_ACCESS

[tanersener]

FFmpeg operations fail with EXC_BAD_ACCESS on ff_hscale_8_to_15_neon function.

All iOS devices with arm64 architecture (probably arm64e as well), running v4.3.1 and v4.3.1.LTS releases, are affected from this.

The crash is caused by ffmpeg commit bd831912712e32b8e78d409bfa7ea7e668ce4b42.

[tanersener]

This issue is fixed using the previous version of libswscale/aarch64/hscale.S file.

[alexcohn]

does this problem apply to Android at all?

[tanersener]

I'm not sure. Unfortunately, I couldn't test it. I don't have a working arm64 Android device right now. So I'm using the same workaround for Android as well.

[alexcohn]

Have you got a test case to prove it? I have some arm64 here to run such test. Also, the device is rather old, so if it works there, it will also work on more advanced devices.

[tanersener]

Yes, I do. It is pretty easy actually.

On iOS, it is possible to reproduce it using the test-application. If I test "mp4" encoding under the "Video" tab, library crashes with EXC_BAD_ACCESS.

I think the same scenario can be tested using the Android test app. Both Android/iOS applications use the same commands for encoding. So if the same bug is there, it will crash there too.

It'd be great if you can test this.

[alexcohn]

If I test "mp4" encoding under the "Video" tab, library crashes with EXC_BAD_ACCESS.

I tested it on my Android arm64 device (BV-6000) and it a) works correctly, and b) I proved that this ff_hscale_8_to_15_neon function is actually called (an artificial div by 0 caused the expected crash).

So, I propose to mark this patch iOS only. After all, the claim on https://git.ffmpeg.org/gitweb/ffmpeg.git/commit/bd831912712e32b8e78d409bfa7ea7e668ce4b42 is that this gives 25% improvement, which is not something one can dismiss lightheartedly.

[tanersener]

Thanks for testing this case. Yes, we can mark this patch iOS only. I will update android-ffmpeg.sh and remove the patch. This change will be included in the next Main release.