This content has not been validated; it was AI-generated following the x86-64 ISA Documentation generation process to maintain high quality. However, as no human has verified this data, errors may exist. If the accuracy of this data is critical, please consult the Intel SDM. The model used to generate this is gemma4:31b

KMOVB

Copies a byte from a source to a destination based on the value of a mask register. The operation is performed for each byte element of the destination; if the corresponding bit in the mask register is set, the byte is copied; otherwise, the destination byte remains unchanged.

The table after the description covers what the source and destinations can be.

DO NOT support LOCK

This instruction is only available when the processor is operating in 64-bit mode or compatibility mode and requires the AVX-512 foundation extensions. It operates on vector registers (zmm/ymm/xmm) and requires the use of opmask registers (k0-k7).

The mask register MUST be specified to avoid undefined behavior regarding the elements not targeted by the mask. If the destination is a memory operand, the memory region MUST be properly aligned to the vector size to avoid performance degradation or alignment check exceptions. Failure to use a valid mask register will result in the instruction failing to update the intended target elements.