如何判断 x86 指令的长度? [英] How to tell the length of an x86 instruction?

问题描述

我正在查看汇编中的不同指令，但我对如何决定不同操作数和操作码的长度感到困惑.

这是您应该从经验中知道的，还是有办法找出哪个操作数/运算符组合占用了多少字节?

例如:

push %ebp ;占用一个字节mov %esp, %ebp ;占用两个字节

所以问题是:

看到给定的指令后，我如何推断其操作码需要多少字节?

解决方案

没有数据库的 x86 没有硬性规定，因为指令编码非常复杂(并且操作码本身可以从 1 到 3 个字节不等).您可以查阅

I was looking at the different instructions in assembly and I am confused on how the lengths of different operands and opcodes are decided upon.

Is it something you ought to know from experience, or is there a way to find out which operand/operator combination takes up how many bytes?

For eg:

push %ebp ; takes up one byte
mov %esp, %ebp ; takes up two bytes

So the question is:

Upon seeing a given instruction, how can I deduce how many bytes its opcode will require?

解决方案

There's no hard and fast rule for x86 without a database as the instruction encoding is pretty complex (and the opcode itself can vary from 1 to 3 bytes). You can consult the Intel® 64 and IA-32 Architectures Software Developer’s Manual 2A document (Chapter 2: Instruction Format) to see how instructions and their operands are encoded:

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