如何从MIPS中的主函数返回值? [英] How do I return a value from the main function in MIPS?

问题描述

说我想在MIPS中编写以下C程序:

Say I want to write the following C program in MIPS:

int main () {
  return 5;
}

当我在 MARS 中尝试以下MIPS代码时:

When I try the following MIPS code in MARS:

main:   ADDI $v0, $zero, 5     # $v0 = 5
        JR $ra                 # return from main()

我收到无效的程序计数器"错误.这显然是因为您无法跳出MARS的主要功能.所以我尝试像这样重写它:

I get a 'invalid program counter' error. This is apparently because you cannot jump out of the main function in MARS. So I tried rewriting it like so:

main:   ADDI $v0, $zero, 5     # $v0 = 5
        li $v0, 10             # load 10(exit) for syscall
        syscall                # exit

执行此操作后，$ v0寄存器包含值10，而不是5.这是可以理解的，因为我必须重写$ v0寄存器才能使syscall正常工作.那么，我的问题是，应在哪里保存值5以便将其正确返回给此应用程序的调用者?

After executing this, the $v0 register contains the value 10, not 5. Which is understandable since I had to overwrite the $v0 register in order for syscall to work. My question, then, is where would I save the value 5 in order for it to be returned to the caller of this application correctly?

推荐答案

使用系统调用17 :

exit2 (terminate with value)
----------------------------
$v0 = 17
$a0 = termination result

请注意如果MIPS程序在MARS图形界面(GUI)的控制下运行，则$ a0中的退出代码将被忽略."

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