lock cmpxchg指令

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最新推荐文章于 2025-03-30 10:19:48 发布

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本文深入探讨了CMPXCHG指令，包括其用途、工作原理及如何使用。通过详细解释，帮助读者掌握如何在编程中利用这一重要的CPU指令实现数据比较与交换。

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CMPXCHG - Compare and Exchange
0F B0/ r     CMPXCHG r/m8,r8     Compare AL with r/m8. If equal, ZF is set and r8 is loaded
          into r/m8. Else, clear ZF and load r/m8 into AL.
0F B1/ r     CMPXCHG r/m16,r16   Compare AX with r/m16. If equal, ZF is set and r16 is
          loaded into r/m16. Else, clear ZF and load r/m16 into AL
0F B1/ r     CMPXCHG r/m32,r32   Compare EAX with r/m32. If equal, ZF is set and r32 is
          loaded into r/m32. Else, clear ZF and load r/m32 into AL

Description
Compares the value in the AL, AX, or EAX register (depending on the size of the operand) with the first operand (destination operand). If the two values are equal, the second operand (source operand) is loaded into the destination operand. Otherwise, the destination operand is loaded into the AL, AX, or EAX register.

This instruction can be used with a LOCK prefix to allow the instruction to be executed atomi-cally. To simplify the interface to the processor's bus, the destination operand receives a write cycle without regard to the result of the comparison. The destination operand is written back if the comparison fails; otherwise, the source operand is written into the destination. (The processor never produces a locked read without also producing a locked write.)