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Top-byte Ignore (TBI) - ARM
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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.

See also


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