LOCK Prefix (lock) Intel X86 IA-32 Assembly Language Reference Manual

LOCK Prefix (lock)

lock

Operation

LOCK# -> NEXT Instruction

Description

The LOCK # signal is asserted during execution of the instruction following the lock prefix. This signal can be used in a multiprocessor system to ensure exclusive use of shared memory while LOCK # is asserted. The bts instruction is the read-modify-write sequence used to implement test-and-run.

The lock prefix works only with the instructions listed here. If a lock prefix is used with any other instructions, an undefined opcode trap is generated.

Memory field alignment does not affect the integrity of lock.

If a different 80386 processor is concurrently executing an instruction that has a characteristic listed here, locked access is not guaranteed. The previous instruction:

• Does not follow a lock prefix
• Is not on the previous list of acceptable instructions
• A memory operand specified has a partial overlap with the destination operand.

Example

lock