结合中断上下文切换和进程上下文切换分析Linux内核的一般执行过程

#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
int main (){
          pid_t pid;
          pid = fork();
          if (pid < 0){
                  printf("error in fork!\n");
          }
          else if (pid == 0){
                  printf("i am the child process, my process id is %d\n",getpid());
          }
          else{
                  printf("i am the parent process, my process id is %d\n",getpid());
         }
         return 0;
}

long do_fork(unsigned long clone_flags,
    unsigned long stack_start,
    unsigned long stack_size,
    int __user *parent_tidptr,
    int __user *child_tidptr)
{
    struct task_struct *p;
    int trace = 0;
    long nr;

    /*
    * Determine whether and which event to report to ptracer.  When
    * called from kernel_thread or CLONE_UNTRACED is explicitly
    * requested, no event is reported; otherwise, report if the event
    * for the type of forking is enabled.
    */
    if (!(clone_flags & CLONE_UNTRACED)) {
        if (clone_flags & CLONE_VFORK)
            trace = PTRACE_EVENT_VFORK;
        else if ((clone_flags & CSIGNAL) != SIGCHLD)
            trace = PTRACE_EVENT_CLONE;
        else
            trace = PTRACE_EVENT_FORK;
    
        if (likely(!ptrace_event_enabled(current, trace)))
            trace = 0;
    }
    
    p = copy_process(clone_flags, stack_start, stack_size,
        child_tidptr, NULL, trace);
    /*
    * Do this prior waking up the new thread - the thread pointer
    * might get invalid after that point, if the thread exits quickly.
    */
    if (!IS_ERR(p)) {
        struct completion vfork;
        struct pid *pid;
    
        trace_sched_process_fork(current, p);
    
        pid = get_task_pid(p, PIDTYPE_PID);
        nr = pid_vnr(pid);
    
        if (clone_flags & CLONE_PARENT_SETTID)
            put_user(nr, parent_tidptr);
    
        if (clone_flags & CLONE_VFORK) {
            p->vfork_done = &vfork;
            init_completion(&vfork);
            get_task_struct(p);
        }
    
        wake_up_new_task(p);
    
        /* forking complete and child started to run, tell ptracer */
        if (unlikely(trace))
            ptrace_event_pid(trace, pid);
    
        if (clone_flags & CLONE_VFORK) {
            if (!wait_for_vfork_done(p, &vfork))
                ptrace_event_pid(PTRACE_EVENT_VFORK_DONE, pid);
        }
    
        put_pid(pid);
    } else {
        nr = PTR_ERR(p);
    }
    return nr;

}

#include <unistd.h>  
  
int main(int arg,char **args)  
{  
    //char *name="/usr/bin/ls";  
    char *argv[]={"ls","-l","/home/shiyanlou/Desktop",NULL};  
    char *envp[]={0,NULL};
    execve("/bin/ls",argv,envp);  
}  

#define switch_to(prev,next,last) do {                    
    asm volatile(
        "pushl %%esi\n\t""pushl %%edi\n\t""pushl %%ebp\n\t""movl %%esp,%0\n\t"    /* save ESP */"movl %3,%%esp\n\t"    /* restore ESP */"movl $1f,%1\n\t"        /* save EIP */"pushl %4\n\t"        /* restore EIP */"jmp __switch_to\n""1:\t""popl %%ebp\n\t""popl %%edi\n\t""popl %%esi\n\t"                    
        :"=m" (prev->thread.esp), "=m" (prev->thread.eip), 
        "=b" (last)                    
        :"m" (next->thread.esp), "m" (next->thread.eip), 
        "a" (prev), "d" (next), 
        "b" (prev));                    
} while (0)