64-bit ARM architecture and instruction set
The 64-bit version of the ARM architecture, named AArch64, was announced in 2011. This architecture has 31 general-purpose 64-bit registers, 64-bit addressing, a 48-bit virtual address space, and a new instruction set named A64.
The 64-bit instruction set is a superset of the 32-bit instruction set, allowing existing 32-bit code to run unmodified on 64-bit processors.
Instructions are 32 bits wide, and most operands are 32 or 64 bits. The A64 register functions differ in some respects from 32-bit mode: the program counter is no longer directly accessible as a register and an additional register is provided that always returns an operand value of zero.
At the user privilege level, most A64 instructions have the same mnemonics as the corresponding 32-bit instructions. The assembler determines whether an instruction operates on 64-bit or 32-bit data based on the operands provided. The following rules determine the operand length...
