Makefile

# 编译器和汇编器
CC      = gcc
NASM    = nasm

# 编译、汇编和链接选项
# -nostdlib 和 -nostartfiles 用于防止引入系统启动文件和标准库
CFLAGS  = -static -O2 -nostdlib -nostartfiles -Wall -Wextra -m64
LDFLAGS = -static -m64 -nostdlib -nostartfiles
ASMFLAGS = -f elf64

# 目标文件和生成的可执行文件名
TARGET  = mysh
OBJS    = mysh.o syscalls.o

all: $(TARGET)

$(TARGET): $(OBJS)
	$(CC) $(LDFLAGS) -o $@ $(OBJS)

mysh.o: mysh.c
	$(CC) $(CFLAGS) -c -o $@ mysh.c

syscalls.o: syscalls.asm
	$(NASM) $(ASMFLAGS) -o $@ syscalls.asm

clean:
	rm -f $(TARGET) $(OBJS)

mysh.c

#define _GNU_SOURCE
#include <sys/types.h>
#define NULL ((void*)0) // 手动定义 NULL

// 声明汇编函数
ssize_t syscall_read(int fd, void* buf, size_t count);
ssize_t syscall_write(int fd, const void* buf, size_t count);
pid_t syscall_fork(void);
int syscall_execve(const char* path, char* const argv[], char* const envp[]);
pid_t syscall_wait4(int pid, int* status, int options, void* rusage);
void syscall_exit(int status);

#define MAX_ARGS 64
#define MAX_LINE 1024

// 自定义简单参数分割
int split_args(char* line, char** args)
{
    int i = 0;
    while (*line != '\0' && i < MAX_ARGS - 1)
    {
        while (*line == ' ')
            *line++ = '\0';
        if (*line)
            args[i++] = line;
        while (*line && *line != ' ')
            line++;
    }
    args[i] = NULL;
    return i;
}

void _start()
{
    char cmd[MAX_LINE];
    char* args[MAX_ARGS];

    const char prompt[] = "mysh> ";

    while (1)
    {
        syscall_write(1, prompt, sizeof(prompt) - 1);

        ssize_t len = syscall_read(0, cmd, MAX_LINE);
        if (len <= 0)
            syscall_exit(1);
        cmd[len - 1] = '\0'; // 去掉换行符

        if (!split_args(cmd, args))
            continue;
        if (args[0][0] == 'e' && args[0][1] == 'x' && args[0][2] == 'i'
            && args[0][3] == 't' && args[0][4] == '\0')
        {
            syscall_exit(0);
        }

        pid_t pid = syscall_fork();
        if (pid == 0)
        { // 子进程
            syscall_execve(args[0], args, NULL);
            const char err[] = "execve failed\n";
            syscall_write(2, err, sizeof(err) - 1);
            syscall_exit(1);
        }
        else if (pid > 0)
        { // 父进程
            syscall_wait4(pid, NULL, 0, NULL);
        }
    }
}

syscalls.asm

; syscalls.asm
section .text
global syscall_read, syscall_write, syscall_execve
global syscall_fork, syscall_wait4, syscall_exit

; ssize_t syscall_read(int fd, void *buf, size_t count)
syscall_read:
    mov rax, 0      ; sys_read
    syscall
    ret

; ssize_t syscall_write(int fd, const void *buf, size_t count)
syscall_write:
    mov rax, 1      ; sys_write
    syscall
    ret

; pid_t syscall_fork(void)
syscall_fork:
    mov rax, 57     ; sys_fork
    syscall
    ret

; int syscall_execve(const char *filename, char *const argv[], char *const envp[])
syscall_execve:
    mov rax, 59     ; sys_execve
    syscall
    ret

; pid_t syscall_wait4(int pid, int *status, int options, struct rusage *rusage)
syscall_wait4:
    mov rax, 61     ; sys_wait4
    syscall
    ret

; void syscall_exit(int status)
syscall_exit:
    mov rax, 60     ; sys_exit
    syscall