You might also want to checkout the Assembly books by Larry Pyeatt (ARM only) and Daniel Kusswurm (x86 + ARM). Another excellent classic which you should check

You might also want to checkout the Assembly books by Larry Pyeatt (ARM only) and Daniel Kusswurm (x86 + ARM). Another excellent classic which you should checkout if you are interested in all things ARM is ARM System Developer's Guide: Designing and Optimizing System Software by Sloss, Symes and Wright. It is old and so does not cover newer ARM architectures but will give you a solid foundation for system programming.