If you have previously flashed any version of a Sony-Open-Devices-based ROM
from before December 17th 2018, your dsp partition might have wrong
SELinux labels and you might thus have problems with audio.
Short version
Either re-flash the dsp partition with stock firmware via Sony’s own
Emma or the open-source FlashTool, or manually force
the correct file labels. You need to be root via adb shell or in recovery:
su
# It might be either /system/vendor/dsp or /vendor/dsp depending on your device
# Just try both until one succeeds
mount -o remount,rw /system/vendor/dsp
chcon -R u:object_r:adsprpcd_file:s0 /dsp
Reboot, et voilà - you should have proper audio again.
If you only want to fix your audio problem, you can stop reading now.
Long version
Sony devices have a dsp partition that holds firmware files and libraries
needed for the Qualcomm “Hexagon” DSP - Digital Signal Processor.
The partition is shippped with the SELinux file label
u:object_r:adsprpcd_file:s0 by default, and stock firmware uses this label
as well when flashed via Emma or FlashTool.
When stellirin rewrote the SODP sepolicy in late 2017, they
chose to use qdsp_file instead of adsprpcd_file for /dsp.
A few lines of code were added in init.$device.rc - which gets
run under the label vendor_init - to re-mount the dsp partition and update it
to use the qdsp_file label.
Because re-labeling these files as vendor_init is a
neverallow in Pie, we noticed that we should rather be
re-using the stock file labels, i.e. adsprpcd_file.
The relabeling bit(restorecon_recursive) was removed
from its new location in init.common.rc and the “new” old label
was restored.
As stated in the “short version”, fixing the problem is easy: Run chcon or run
Emma - Emma can now flash single partitions, which is great.
Conclusion
A small inconsistency can cause a whole lot of trouble. Who could have predicted
back in 2017 that Google would tighten the security around re-labeling files?
The transition is going to be a bit painful, but in the end, re-using
adsprpcd_file is the better solution.