什么！在ARM组装中扮演角色? [英] What does the ! character do in ARM assembly?

问题描述

#include <stdio.h>
void fun();
int main()
{
        int a = 10;
        fun();
        return 0;

}
void fun()
{
    int a =  5;
}

汇编代码.

000103e4 <main>:
   103e4:       e52db008        str     fp, [sp, #-8]!
   103e8:       e58de004        str     lr, [sp, #4]
   103ec:       e28db004        add     fp, sp, #4
   103f0:       e24dd008        sub     sp, sp, #8
   103f4:       e3a0300a        mov     r3, #10
   103f8:       e50b3008        str     r3, [fp, #-8]
   103fc:       eb000005        bl      10418 <fun>
   10400:       e3a03000        mov     r3, #0
   10404:       e1a00003        mov     r0, r3
   10408:       e24bd004        sub     sp, fp, #4
   1040c:       e59db000        ldr     fp, [sp]
   10410:       e28dd004        add     sp, sp, #4
   10414:       e49df004        pop     {pc}            ; (ldr pc, [sp], #4)

00010418 <fun>:
   10418:       e52db004        push    {fp}            ; (str fp, [sp, #-4]!)
   1041c:       e28db000        add     fp, sp, #0
   10420:       e24dd00c        sub     sp, sp, #12
   10424:       e3a03005        mov     r3, #5
   10428:       e50b3008        str     r3, [fp, #-8]
   1042c:       e1a00000        nop                     ; (mov r0, r0)
   10430:       e24bd000        sub     sp, fp, #0
   10434:       e49db004        pop     {fp}            ; (ldr fp, [sp], #4)
   10438:       e12fff1e        bx      lr

在上面的汇编代码中 103e4:e52db008 str fp，[sp，#-8]！

In a above assembly code 103e4: e52db008 str fp, [sp, #-8]!

我是汇编语言的新手. 为什么 '！'已经被用了什么目的.

I am new to assembly language. why '!' has been used what is the purpose.

推荐答案

ARM汇编代码中的!表示地址寄存器已更新. (这非常令人兴奋！)在str fp, [sp, #-8]!中，将<8>添加到sp，然后将fp的内容存储在sp中的新地址处.如果!不存在，则fp仍将存储在同一地址，但sp不会被更新.

That ! in ARM assembly code means the address register is updated. (It is very exciting!) In str fp, [sp, #-8]!, −8 is added to sp, and then the contents of fp are stored at the new address in sp. If the ! were not present, fp would still be stored at the same address, but sp would not be updated.

有一条相应的指令，您可以在代码ldr fp, [sp], #4的其他地方看到.以这种形式，fp的内容存储在sp中的地址，然后将4添加到sp.

There is a corresponding instruction which you see elsewhere in the code, ldr fp, [sp], #4. In this form, the contents of fp are stored at the address in sp, and then 4 is added to sp.

第一种形式通常用于将事物压入堆栈:递减堆栈指针以为堆栈中的新事物腾出空间，然后写入该值.第二种形式用于弹出:读取堆栈上的值，然后递增堆栈指针，从而有效地从堆栈的活动部分中删除空间.

The first form is commonly used for pushing things onto the stack: The stack pointer is decremented to make room for new things on the stack, and then the value is written. The second form is used for popping: The value on the stack is read, and then the stack pointer is incremented, effectively removing the space from the live part of the stack.

它们也可以用于遍历数组，加载或存储元素以及移动指针，而无需单独的指令来加载/存储和更改指针.

They can also be used to iterate through an array, loading or storing elements and moving the pointer without needing separate instructions for loading/storing and changing the pointer.

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