According to most user reports, everything runs smooth and the newest firmware improved quite a few things without breaking others. But despite this, custom ROM and kernel developers weren’t able to get their hands on the open source files required for development. Having working source code definitely eases the process of porting new Android versions and ironing out existing bugs. Luckily, Sony complied with its GPL requirements and released the related files for kernel 3.4 in a timely fashion. The open source goods can be obtained from the official website as tar.bz2 package:
Kernels based on these files can be built with GCC 4.7 toolchain, which is available in Android’s source. If you want to build your own kernel, head over to the XDA University to find a comprehensive guide to get started with kernel development.