我有一个基础的问题 [英] i have a based question

问题描述

这本书描述了推送:

The book described the Push:

因此，将双字值压入堆栈需要先减小
堆栈指针减4，然后将值写入新的堆栈地址顶部.因此，说明
pushl％ebp与以下指令对具有相同的行为:
subl $ 4 ，％esp
movl％ebp，(％esp)

Pushing a double-word value onto the stack therefore involves first decrementing the
stack pointer by 4 and then writing the value at the new top of stack address. Therefore, the instruction
pushl %ebp has equivalent behavior to the following pair of instructions:
subl $4,%esp
movl %ebp,(%esp)

我只想知道为什么4而不是2 8?

请给我一些建议.

谢谢

I just want to know why 4 , not 2, 8?

Please give me some advices.

Thank you

推荐答案

4 ，％esp
movl％ebp，(％esp)

4,%esp
movl %ebp,(%esp)

我只想知道为什么4而不是2、8?

请给我一些建议.

谢谢

I just want to know why 4 , not 2, 8?

Please give me some advices.

Thank you

这是4，因为本书所引用的处理器使用的是标准"尺寸.

字是两个字节，因此双字是4个字节.

因此，为了在堆栈上留出空间，必须将指针减少4个字节-双字的大小.

It is 4 because the processor that the book was referencing used ''standard'' sizes.

A word is two bytes and a double-word is therefore 4 bytes.

Therefore to allow room on the stack the pointer has to be decreased by 4 bytes - the size of a double-word.

因为long(至少在32位上)机器)的长度为4个字节...
:)

Because a long (at least on a 32 bit machine) is 4 bytes long...
:)

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