ARM ISA

General

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Variants

26-bit 32-bit 64-bit

Extensions

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Topics

Addressing Modes Registers Assembly Interrupts CPSR Modes Calling Convention Microarchitectures

Versions(all)

ARMv1 ARMv2 ARMv2a ARMv3 ARMv4 ARMv5 ARMv6 ARMv7 ARMv8 ARMv8.1 ARMv8.2 ARMv8.3

AArch64 is the 64-bit execution state of the ARMv8 ISA. A machine in this state executes operates on the A64 instruction set. This is in contrast to the AArch32 which describes the classical 32-bit ARM execution state.

Overview

The AArch64 execution state was introduced with the ARMv8 ISA for machines executing A64 instructions. A machine in AArch64 can only execute A64 instructions and cannot execute A32 or T32 instructions. However, unlike in AArch32, in the 64-bit state, instructions can access both the 64-bit and 32-bit registers.

Calling convention

See also: calling convention

Under AArch64, the first eight registers are used for passing parameters into a subroutine as well as to return a result value set. Generally, X0 through X18 can corrupt while X19-X29 must be preserved.

Register	Role	Requirement
X0 - X7	Parameter/result registers	Can Corrupt
X8	Indirect result location register
X9 - X15	Temporary registers
X16 - X17	Intra-procedure call temporary
X18	Platform register, otherwise temporary
X19 - X29	Callee-saved register	Must preserve
X30	Link Register	Can Corrupt

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