结合中断上下文切换和进程上下文切换分析Linux内核一般执行过程

1 long _do_fork(struct kernel_clone_args *args) 
2 { 
3 　　　　　　　　　　　　　　　　　　//复制进程描述符和执?时所需的其他数据结构
4 　　p = copy_process(NULL, trace, NUMA_NO_NODE, args); 
5 　　wake_up_new_task(p);　　　　//将?进程添加到就绪队列
6 　　return nr;　　　　　　　　　　//返回?进程pid（?进程中fork返回值为?进程的pid） 
7 }

1 int sys_execve(const char *filename, char *const argv[], char *const envp[])
2 {
3 　　return my_syscall3(__NR_execve, filename, argv, envp);
4 }

 1 #include <stdio.h>
 2 #include <stdlib.h>
 3 
 4 #include <sys/types.h>
 5 #include <unistd.h>
 6 
 7 int main(void)
 8 {
 9     const char *oldpath = "execl_ln.c";
10     const char *newpath = "a.c";
11     int count = 1;
12     int child;
13 
14     child = fork();
15 
16     if (child < 0)
17     {
18         perror("error fork");
19     }
20     else if (child == 0)
21     {
22         execlp("ls", "ls", NULL);
23         printf("Child process  : %d (%p), %d\n", ++count, &count, getpid());
24     }
25     else
26     {
27         printf("Parent process : %d (%p), %d\n", count, &count, getpid());
28     }
29 
30     return EXIT_SUCCESS;
31 }

1 Parent process : 1 (0x7ffee5ab97d4), 11041
2 a
3 a.c
4 execl_ln
5 execl_ln.c
6 forktest
7 ln.s

1 int do_execve(struct filename *filename,
2     const char __user *const __user *__argv,
3     const char __user *const __user *__envp)
4 {
5     struct user_arg_ptr argv = { .ptr.native = __argv };
6     struct user_arg_ptr envp = { .ptr.native = __envp };
7     return do_execveat_common(AT_FDCWD, filename, argv, envp, 0);
8 }

1 static int do_execveat_common(int fd, struct filename *filename,
2                   struct user_arg_ptr argv,
3                   struct user_arg_ptr envp,
4                   int flags)
5 {
6     return __do_execve_file(fd, filename, argv, envp, flags, NULL);
7 }

 1 static int __do_execve_file(int fd, struct filename *filename,
 2                 struct user_arg_ptr argv,
 3                 struct user_arg_ptr envp,
 4                 int flags, struct file *file)
 5 {
 6     char *pathbuf = NULL;
 7     struct linux_binprm *bprm;
 8     struct files_struct *displaced;
 9     int retval;
10     /* We‘re below the limit (still or again), so we don‘t want to make
11      * further execve() calls fail. */
12     current->flags &= ~PF_NPROC_EXCEEDED;
13 
14         ......
15 
16     retval = bprm_mm_init(bprm);　　//为ELF文件分配内存

17 
18     would_dump(bprm, bprm->file);
19     retval = exec_binprm(bprm);//开始执行加载到内存中的ELF文件
20     if (retval < 0)
21         goto out;
22 
23     /* execve succeeded */
24 
25     return retval;
26         ......          
27 } 

 1 static int exec_binprm(struct linux_binprm *bprm)
 2 {
 3     pid_t old_pid, old_vpid;
 4        
 5     ......
 6     int ret;
 7     ret = search_binary_handler(bprm);
 8     
 9     ......
10     return ret;
11 }

 1 int search_binary_handler(struct linux_binprm *bprm)
 2 {
 3     bool need_retry = IS_ENABLED(CONFIG_MODULES);
 4     struct linux_binfmt *fmt;
 5     int retval;
 6         
 7         ......
 8     retval = security_bprm_check(bprm);//检查是否具有运行权限
 9     if (retval)
10         return retval;
11 
12     retval = -ENOENT;
13  retry:
14     read_lock(&binfmt_lock);
15     list_for_each_entry(fmt, &formats, lh) {//尝试每一种格式的解析函数

16         if (!try_module_get(fmt->module))
17             continue;
18         read_unlock(&binfmt_lock);
19 
20         bprm->recursion_depth++;
21         retval = fmt->load_binary(bprm);//最关键的步骤，调用合适格式的处理函数加载该可执行文件
22         bprm->recursion_depth--;
23 
24                 .........
25     return retval;
26 }