ARMv8-A / ARMv9-A ecosystem

ARM64 / AArch64

A load/store 64-bit architecture used in phones, Apple Silicon, servers, embedded boards, secure firmware, kernels, and modern performance-sensitive software.

Linux ELFAndroid ELFmacOS/iOS Mach-OFirmware/UEFI

ABI notes

AAPCS64 defines argument registers, callee-saved registers, stack alignment, vector registers, and platform calling rules. Apple arm64 adds platform-specific conventions.

Privilege model

Exception levels EL0-EL3, vector tables, system registers, MMU, barriers, traps, SMC/HVC, pointer authentication on supported platforms.

Registers

Name	Aliases	Class	Role
X0-X7	W0-W7	General	Arguments and return values
X8	W8	General	Indirect result and syscall number on Linux
X9-X15	W9-W15	General	Caller-saved temporaries
X19-X28	W19-W28	General	Callee-saved registers
X29	FP	Stack	Frame pointer
X30	LR	Control	Link register return address
SP	WSP	Stack	Stack pointer
V0-V31	B/H/S/D/Q views	SIMD/FP	Floating point and vector work

Instruction groups

Load/store
LDR, STR, LDP, STP, addressing modes, literals

Arithmetic and logic
ADD, SUB, AND, ORR, EOR, shifts, bitfield ops

Branching
B, BL, RET, CBZ, CBNZ, TBZ, TBNZ, conditional branches

System
MRS, MSR, SVC, HVC, SMC, ISB, DSB, DMB

Atomics/SIMD
LDXR/STXR, acquire/release, NEON, SVE where available

Starter code

.global _start
_start:
    mov x8, #64
    mov x0, #1
    adr x1, msg
    mov x2, #12
    svc #0

    mov x8, #93
    mov x0, #0
    svc #0
msg:
    .ascii "hello arm64\n"