《linux 内核完全剖析》 signal.c 代码分析笔记

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signal.c 代码分析笔记

sgetmask


int sys_sgetmask()// 获取当前进程阻塞的信号
{returncurrent->blocked;
}

sys_ssetmask


int sys_ssetmask(int newmask) //设置当前进程阻塞信号,确保SIGKILL 和SIGSTOP不被阻塞
{int old=current->blocked;current->blocked= newmask & ~(1<<(SIGKILL-1)) & ~(1<<(SIGSTOP-1));return old;
}

sys_sigpending


int sys_sigpending(sigset_t *set)//verify_area的水有点深。嘿嘿。。。
{/* fill in "set" with signals pending but blocked. */verify_area(set,4); //验证set指向的地址处4字节是否可写，不可写就给他分配一页内存，并给与读写权限。。。。put_fs_long(current->blocked & current->signal, (unsigned long*)set); //这里理解成把第一个参数的值赋值给set指向的地址就好。。。。return 0;
}

put_fs_byte


extern inline void put_fs_byte(charval,char *addr)
{__asm__ ("movb%0,%%fs:%1"::"r" (val),"m" (*addr));}

需要说明的就是这里fs寄存器是指向LDT的数据段描述符0x17，即fs用于访问数据

sys_sigsuspend


int sys_sigsuspend(int restart, unsignedlong old_mask, unsigned long set)
{extern int sys_pause(void); //声明引用sys_pauseif (restart) {//如果restart 非零，进程的阻塞信号为old_mask/*we're restarting */current->blocked= old_mask;return-EINTR;}//如果restart 非零/* we're not restarting.  do thework */*(&restart) = 1;*(&old_mask) = current->blocked; //把当前进程的阻塞信号做oldmask//额。。。我不知道给一个局部变量赋值之后又不返回，先的函数也不引用这变量，//这究竟有什么用！我必须质疑这是冗余的赋值操作current->blocked = set;(void) sys_pause();                     /*return after a signal arrives *///我不得不感叹，这个sys_pause就相当于sleep(很短的时间)//这么做就是为了捕获信号return -ERESTARTNOINTR;               /*handle the signal, and come back */
}

save_old


static inline void save_old(char *from,char * to) //把内核段的数据copy到用户段(local date space)
{inti;verify_area(to,sizeof(struct sigaction)); //确保to地址处有结构体大小的内存可读写for(i=0 ; i< sizeof(struct sigaction) ; i++) { //一个字节一个字节的copy,from到toput_fs_byte(*from,to);from++;to++;}
}

get_new


static inline void get_new(char * from,char* to)//把数据从用户段copy到内核数据段中
{inti;for(i=0 ; i< sizeof(struct sigaction) ; i++)*(to++)= get_fs_byte(from++);
}

sys_signal


int sys_signal(int signum, long handler,long restorer)
{structsigaction tmp;if(signum<1 || signum>32 || signum==SIGKILL || signum==SIGSTOP)//常规检测，signal必须在定义范围内，并且不能呢个为SIGKILL和SIGSTOP，否者直接结束return-EINVAL;tmp.sa_handler= (void (*)(int)) handler; //handler被强制转换成了一个函数指针,这个函数以int为参数，无返回tmp.sa_mask= 0;//清空所有信号tmp.sa_flags= SA_ONESHOT | SA_NOMASK;tmp.sa_restorer= (void (*)(void)) restorer; //restorer被强制转换成一个函数指针,这个函数以int为参数，无返回handler= (long) current->sigaction[signum-1].sa_handler;current->sigaction[signum-1]= tmp; //结构体直接赋值return handler;
}

sys_sigaction


int sys_sigaction(int signum, const structsigaction * action,structsigaction * oldaction)
{structsigaction tmp;if(signum<1 || signum>32 || signum==SIGKILL || signum==SIGSTOP)//常规检测，signal必须在定义范围内，并且不能呢个为SIGKILL和SIGSTOP，否者直接结束return-EINVAL;tmp= current->sigaction[signum-1];get_new((char*) action,(char*) (signum-1+current->sigaction)); //把只读的action结构体的信息写入到内核数据段if(oldaction)save_old((char*) &tmp,(char *) oldaction); //current进程原来的sigaction结构体信息if(current->sigaction[signum-1].sa_flags & SA_NOMASK) //如果要求信号清零current->sigaction[signum-1].sa_mask= 0;//信号清零elsecurrent->sigaction[signum-1].sa_mask|= (1<<(signum-1)); //否则把signum 写入信号变量return0;}

do_signal


int do_signal(long signr,long eax,long ebx,long ecx, long edx, long orig_eax,longfs, long es, long ds,longeip, long cs, long eflags,unsignedlong * esp, long ss)
{unsignedlong sa_handler;longold_eip=eip;structsigaction * sa = current->sigaction + signr - 1;int longs;unsignedlong * tmp_esp;#ifdef notdefprintk("pid:%d, signr: %x, eax=%d, oeax = %d, int=%d\n",current->pid,signr, eax, orig_eax,sa->sa_flags& SA_INTERRUPT); //打印相关信息#endifif((orig_eax != -1) && //如果不是系统调用而是其他中断执行过程中调用到本函数时，roig_eax 值为-1((eax == -ERESTARTSYS) || (eax ==-ERESTARTNOINTR))) {if((eax == -ERESTARTSYS) && ((sa->sa_flags & SA_INTERRUPT) ||signr < SIGCONT || signr > SIGTTOU))*(&eax)= -EINTR;else{*(&eax)= orig_eax;*(&eip)= old_eip -= 2;//不明白为什么这里要回调两个byte}}sa_handler= (unsigned long) sa->sa_handler;if(sa_handler==1)return(1);   /* Ignore, see if there are more signals...*/if(!sa_handler) { //sa_handler 为SIG_DFL 0switch(signr) {caseSIGCONT:caseSIGCHLD:return(1);  /* Ignore, ... */caseSIGSTOP:caseSIGTSTP:caseSIGTTIN:caseSIGTTOU:current->state= TASK_STOPPED; //SIGSTOP SIGTSTP SIGTTIN SIGTTOU 被捕捉了，那么把当前进程置为停止状态current->exit_code= signr;if(!(current->p_pptr->sigaction[SIGCHLD-1].sa_flags &SA_NOCLDSTOP))// 如果parent process 不允许child process stopcurrent->p_pptr->signal|= (1<<(SIGCHLD-1)); //告诉parent ,child process 挂掉了return(1);  /* Reschedule another event */caseSIGQUIT:caseSIGILL:caseSIGTRAP:caseSIGIOT:caseSIGFPE:caseSIGSEGV:if(core_dump(signr))do_exit(signr|0x80);/*fall through */default:do_exit(signr);}}/** OK, we're invoking a handler*/if(sa->sa_flags & SA_ONESHOT)sa->sa_handler= NULL;*(&eip)= sa_handler;longs= (sa->sa_flags & SA_NOMASK)?7:8;//堆栈指针向下偏移7 或者8 ,这时候 longs是 long型变量，esp也是，减去7，8也就是数值上的而已//但是我没想明白这个78的单位是什么？？？ 这又不是指针，所以我就觉得很奇怪。。。。*(&esp)-= longs;verify_area(esp,longs*4);tmp_esp=esp;//各种从用户数据段copy到内核数据段put_fs_long((long)sa->sa_restorer,tmp_esp++);put_fs_long(signr,tmp_esp++);if(!(sa->sa_flags & SA_NOMASK))put_fs_long(current->blocked,tmp_esp++);put_fs_long(eax,tmp_esp++);put_fs_long(ecx,tmp_esp++);put_fs_long(edx,tmp_esp++);put_fs_long(eflags,tmp_esp++);put_fs_long(old_eip,tmp_esp++);current->blocked|= sa->sa_mask;return(0);                   /* Continue, execute handler*/}