Linux操作系统分析Lab1

[weixin_45662787]

实验目标

将一个简单的C程序汇编成LoongArch或RISC-V汇编代码，并逐步分析程序的执行过程，深入理解存储程序计算机和函数调用堆栈框架在执行过程中所起的作用。

实验步骤

1.安装RISC-V的交叉编译器

sudo apt-get install gcc-riscv64-linux-gnu

2.编写一个简单的c程序

#include<stdio.h>
  
int add(int a, int b) {
        return a + b;
}
int main() {
        int a = 7;
        int b = 5;
        int c = add(a, b);
        return 0;
}

3.将c程序汇编成riscv的汇编代码并分析 

        .file   "main.c"
        .option pic
        .text
        .align  1
        .globl  add
        .type   add, @function
add:
        addi    sp,sp,-32         # sp = sp - 32 栈指针减8Byte
        sd      s0,24(sp)         # *(sp + 24) = s0 将s0(main的栈底)存入(sp + 24)
        addi    s0,sp,32          # s0 = sp + 32 
        mv      a5,a0             # a5 = a0
        mv      a4,a1             # a4 = a1
        sw      a5,-20(s0)        # *(s0 - 20) = a5
        mv      a5,a4             # a5 = a4
        sw      a5,-24(s0)        # *(s0 - 24) = a5
        lw      a4,-20(s0)        # a4 = *(s0 - 20)  a4=7
        lw      a5,-24(s0)        # a5 = *(s0 - 24)  a5=5
        addw    a5,a4,a5          # a5 = a4 + a5
        sext.w  a5,a5             # 
        mv      a0,a5             # a0 = a5
        ld      s0,24(sp)         # s0 = *(sp + 24)  栈底回到main的栈底
        addi    sp,sp,32          # sp = sp + 32     栈顶回到main的栈顶
        jr      ra                # 跳转到ra(return address)  main函数的mv a5,a0
        .size   add, .-add
        .align  1
        .globl  main
        .type   main, @function
main:
        addi    sp,sp,-32         # sp = sp - 32
        sd      ra,24(sp)         # *(sp + 24) = ra
        sd      s0,16(sp)         # *(sp + 16) = s0
        addi    s0,sp,32          # s0 = sp + 32
        li      a5,7              # a5 = 7
        sw      a5,-28(s0)        # *(s0 - 28) = a5
        li      a5,5              # a5 = 5
        sw      a5,-24(s0)        # *(s0 - 24) = a5
        lw      a4,-24(s0)        # a4 = *(s0 - 24)
        lw      a5,-28(s0)        # a5 = *(s0 - 28)
        mv      a1,a4             # a1 = a4
        mv      a0,a5             # a0 = a5
        call    add               # 调用add函数，ra的指向下一条指令
        mv      a5,a0             # a5 = a0
        sw      a5,-20(s0)        # *(s0 -20) = a5
        li      a5,0              # a5 = 0
        mv      a0,a5             # a0 = a5
        ld      ra,24(sp)         # ra = *(sp + 24)
        ld      s0,16(sp)         # s0 = *(sp + 16)
        addi    sp,sp,32          # sp = sp + 32
        jr      ra                # 跳转到ra(return address)
        .size   main, .-main
        .ident  "GCC: (Ubuntu 9.4.0-1ubuntu1~20.04) 9.4.0"
        .section        .note.GNU-stack,"",@progbits