retq和ret有什么区别? [英] What is the difference between retq and ret?

问题描述

让我们考虑以下程序，该程序计算参数的无符号平方:

Let's consider the following program, which computes an unsigned square of the argument:

.global foo
.text
foo:
    mov %rdi, %rax
    mul %rdi
    ret

此文件已由as正确编译，但反汇编为

This is properly compiled by as, but disassembles to

0000000000000000 <foo>:
   0:   48 89 f8                mov    %rdi,%rax
   3:   48 f7 e7                mul    %rdi
   6:   c3                      retq   

ret和retq之间是否有区别?

推荐答案

在长(64位)模式下，通过从堆栈中弹出一个四字地址到%rip，您将返回(ret).

In long (64-bit) mode, you return (ret) by popping a quadword address from the stack to %rip.

在32位模式下，通过从堆栈中将双字地址弹出到%eip来返回(ret).

In 32-bit mode, you return (ret) by popping a dword address from the stack to %eip.

某些工具，例如objdump -d调用第一个retq.只是一个名字，指令编码是相同的(C3).

Some tools like objdump -d call the first one retq. It's just a name, the instruction encoding is the same either way (C3).

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