从软件到硬件

00000040: 4111 06e4 22e0 0008 1705 0000 1305 0500
00000050: 9700 0000 e780 0000 8147 3e85 a260 0264
00000060: 4101 8280

main:
        addi    sp,sp,-16
        sd      ra,8(sp)
        sd      s0,0(sp)
        addi    s0,sp,16

0000000000000000 <main>:
   0: 1141        addi sp,sp,-16
   2: e406        sd     ra,8(sp)
   4: e022        sd     s0,0(sp)
   6: 0800        addi s0,sp,16
   8: 00000517    auipc a0,0x0
   c: 00050513    mv a0,a0
  10: 00000097    auipc ra,0x0
  14: 000080e7    jalr ra #10 <main+0x10>
  18: 4781        li a5,0
  1a: 853e        mv a0,a5
  1c: 60a2        ld ra,8(sp)
  1e: 6402        ld s0,0(sp)
  20: 0141        addi sp,sp,16
  22: 8082        ret

gcc ./main.c -S ./main.S

gcc ./main.S -o ./main

while (1) {
  从PC指示的存储器位置取出指令;
  执行指令;
  更新PC;
}

addi x1, x0, 0xf 0x00f00093

#include <sys/syscall.h>
#include <unistd.h>
const char str[] = "\033[01;31mHello, OS World\033[0m\n";
const int str_size = sizeof str - 1;
int main(void) {
  asm volatile("movl %0, %%eax\n\t" // 系统调用号：SYS_write
               "movl $1, %%edi\n\t" // 文件描述符：STDOUT_FILENO (标准输出)
               "movq %2, %%rsi\n\t" // 字符串地址
               "movl %3, %%edx\n\t" // 字符串长度
               "syscall"            // 调用系统调用
               :
               : "r"(SYS_write), "r"(STDOUT_FILENO), "r"(str), "r"(str_size)
               : "eax", "edi", "rsi", "edx");
  return 0;
}

#include <stdio.h>
#include <stdlib.h>
int main(void) {
    int x = 1;
    void *y = malloc(sizeof(int));
    printf("stack: %p\n", (void *)&x);
    printf("heap : %p\n", y);
    free(y);
    return 0;
}

stack: 0x7ffd27bb38dc
heap : 0x59e598fe42a0

enum {
    SYS_EXIT,  // Process exits
    SYS_WRITE, // Write to console with a character
};

typedef struct {
    unsigned int syscall;
    char arg;
} Syscall;

typedef struct {
    int  remainingStep; // A process will run remainingStep steps
    char charToOutput;  // A process will write this character
                        // to console by doing a syscall
} Process; // Process's Context

void run() {
    Process *current;
    while (process_count()) {
        // The Operating System will randomly
        // choose a process to run
        current = process_schedule();
        // Switch process context and run it until a syscall
        Syscall call = process_step(current);
        if (call.syscall == SYS_EXIT) {
            // Process exits
            process_exit(current);
        } else if (call.syscall == SYS_WRITE) {
            // Write the character from syscall arg to the console
            putchar(call.arg);
        }
    }
    putchar('\n');
}

int main() {
    // Initialize the Operating System
    init();
    // spawn processes
    spawn_process(5, 'A');
    spawn_process(5, 'B');
    spawn_process(5, 'C');
    // start running
    run();
    return 0;
}

AABCCCBBBCBCAAA
BBAACCCABBACCAB
CAAACBCCBBAACBB