cmpl和cmp之间的区别 [英] The difference between cmpl and cmp
问题描述
我试图了解程序集以解决难题.但是我遇到了以下指示:
I am trying to understand assembly to be able to solve a puzzle. However I encountered the following instructions:
0x0000000000401136 <+44>: cmpl $0x7,0x14(%rsp)
0x000000000040113b <+49>: ja 0x401230 <phase_3+294>
我认为它的作用是: 0x14(%rsp)的值为-7380.根据我的理解,cmpl比较无符号.同时执行跳转. (unsigned)-7380> 7 (未签名)7380> 7->跳转
What I think its doing is: The value of 0x14(%rsp) is -7380. According to my understanding cmpl compares unsigned. Also the jump is performed. So can it be that (unsigned)-7380 > 7 (unsigned)7380 > 7--> jump
我实际上不希望它跳下去.但这是正确的解释吗?我是在吵架吗?
I actually don't want it to jump. But is this the correct explanation or not? Am I flipping arguments?
如果您对如何操作此跳跃有任何建议!
Also if you have any advice about how to manipulate this jump!
推荐答案
根据我的理解,
cmpl
比较未签名.
在某种程度上,两者都可以.
It does both, in a way.
有符号与无符号的区别在于跳转指令的用法.
The difference in signed vs. unsigned is here the usage of the jump instructions.
对于>
,无符号的为ja
,有符号的为jg
(如果大于则跳转,如果大于则跳转).
For >
, there is ja
for unsigned and jg
for signed (jump if above and jump if greater).
对于<
,无符号的为jb
,有符号的为jl
(如果低于则跳转,如果不足则跳转).
For <
, there is jb
for unsigned and jl
for signed (jump if below and jump if less).
确切地说,这是几个跳转命令的含义:
To be exact, here is the meaning of several jump commands:
对于未签名的比较:
For unsigned comparisons:
JB/JNAE (CF = 1) : Jump if below/not above or equal
JAE/JNB (CF = 0) : Jump if above or equal/not below
JBE/JNA (CF = 1 or ZF = 1) : Jump if below or equal/not above
JA/JNBE (CF = 0 and ZF = 0): Jump if above/not below or equal
对于已签名的比较:
JL/JNGE (SF <> OF) : Jump if less/not greater or equal
JGE/JNL (SF = OF) : Jump if greater or equal/not less
JLE/JNG (ZF = 1 or SF <> OF): Jump if less or equal/not greater
JG/JNLE (ZF = 0 and SF = OF): Jump if greater/not less or equal
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