ARM ISA

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26-bit 32-bit 64-bit

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ARM Thumb ThumbEE Jazelle VFP Neon Helium

Topics

Addressing Modes Registers Assembly Interrupts CPSR Modes Calling Convention Microarchitectures

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

Top-byte ignore (TBI) is a feature introduced with ARMv8 that provides facilities for memory tagging by ignoring the most significant 8 bits of the virtual address.

Overview

Although 64-bit [[[ARM]] registers are 64-bit wide, virtual addresses require that the top 16 bits must either be 0x0000 or 0xFFFF. TBI is a hardware feature, introduced with AArch64, that allows software to use 8 most significant bits of a 64-bit pointer as a tag. This is done by enabling memory tagging support in the Translation Control Register. When enabled, the top eight bits ([63:56]) of the virtual address are ignored.

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