Understanding ARM64 Architecture

Definitions

ARM’s definitions when introducing 64-bit support

• AArch32 – The legacy 32-bit instruction set architecture (ISA) defined by ARM, including Thumb mode execution.
• AArch64 – The new 64-bit ISA (instruction set architecture) defined by ARM.
• ARMv7 - The specification for “7th generation” ARM hardware that also includes support for AArch32. This is the first version of ARM hardware supported by Windows for ARM.
• ARMv8 - The specification for “8th generation” ARM hardware that includes support for both AArch32 and AArch64.

Windows definitions

• ARM – Refers to AArch32 (32-bit ARM architecture), also known as WoA (Windows on ARM).
• ARM32 – Same as ARM above, used in this document for clarity.
• ARM64 – Refers to 64-bit ARM architecture (AArch64). There is no WoA64.

ARM data types

• Short-Vector – A data type that can be directly represented as 8-byte or 16-byte elements in a vector. The size is aligned to 8 or 16 bytes, and each element can be 1, 2, 4, or 8 bytes.
• HFA (Homogeneous Floating-point Aggregate) – A data type containing 2-4 identical floating-point members (floats or doubles).
• HVA (Homogeneous Short-Vector Aggregate) – A data type with 2-4 identical Short-Vector members.

Reference

[1] ARM64 ABI Conventions Overview for C++ Projects on ARM Processors, Microsoft, https://docs.microsoft.com/ko-kr/cpp/build/arm64-windows-abi-conventions?view=msvc-160