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.
|
bt, bts, btr, btc |
m, r/imm |
|
xchg |
r, m |
|
xchg |
m, r |
|
add, or, adc, sbb, and, sub, xor |
m, r/imm |
|
not, neg, inc, dec |
m |
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
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