9. ARM Assembly

In this chapter, we cover the ARM version 8 application profile (ARMv8-A) architecture A64 ISA, the latest ARM ISA that is in use on all Linux OS ARM computers. Recall that an instruction set architecture (or ISA) defines the set of instructions and binary encodings of a machine-level program. To run the examples in this chapter, you will need access to a machine with an ARMv8-A processor with a 64-bit operating system installed. The examples in this chapter use a Raspberry Pi 3B+ running the 64-bit Ubuntu Mate operating system. Note that every Raspberry Pi released since 2016 can use the A64 ISA. However, Raspberry Pi OS (the default Raspberry Pi operating system) is still 32-bit as of this writing.

Readers can confirm that they have a 64-bit version of the OS on their system by running the uname -p command. A system with a 64-bit operating system will output the following:

$ uname -p
aarch64

Although it is possible to build ARM binaries on Intel machines using ARM’s GNU toolchain cross-compilation tools, you cannot run ARM binaries directly on a x86 system. Readers interested in learning about ARM assembly directly on their laptops are encouraged to explore QEMU, which can emulate an ARM system. Emulators differ from virtual machines in that they also simulate the hardware of another system.

Another alternative is to use one of Amazon’s recently released EC2 A1 instances. Each instance gives users access to a 64-bit Graviton processor, which follows the ARMv8-A specification.

Keep in mind, however, that the specific assembly instructions produced by a compiler are highly influenced by the operating system and precise machine architecture. Therefore, the assembly produced on AWS instances or through QEMU emulation may differ slightly from the examples shown in this chapter.

RISC and ARM processors

For many years, complex instruction set computer (CISC) architectures dominated the personal computing and server markets. Common examples of CISC architectures include Intel and AMD processors. However, reduced instruction set computer (RISC) architectures gained momentum over the past decade due to demand from the mobile computing sector. ARM (which stands for Acorn RISC machine) is an example of a RISC architecture, along with RISC-V and MIPS. RISC architectures are especially attractive to mobile computing due to the energy efficiency of their processors, which prolongs battery life. In recent years, ARM and other RISC processors have begun making headway in the server and high performance computing (HPC) markets. For example, Japan’s Fugaku supercomputer, the fastest in the world as of 2020, uses ARM processors.