signal.c

一份精简的linux内核源代码

/*
 *  linux/kernel/signal.c
 *
 *  (C) 1991  Linus Torvalds
 */

#include <linux/sched.h>
#include <linux/kernel.h>
#include <asm/segment.h>

#include <signal.h>

volatile void do_exit(int error_code);

int sys_sgetmask()/*获取当前信号屏蔽位图*/
{
	return current->blocked;
}

int sys_ssetmask(int newmask)/*设置新的信号屏蔽位图*/
{
	int old=current->blocked;

	current->blocked = newmask & ~(1<<(SIGKILL-1));/*SIGKILL不可屏蔽*/
	return old;
}

static inline void save_old(char * from,char * to)/*复制sigaction数据到fs数据段to处。*/
{
	int i;

	verify_area(to, sizeof(struct sigaction));
	for (i=0 ; i< sizeof(struct sigaction) ; i++) {
		put_fs_byte(*from,to);
		from++;
		to++;
	}
}

static inline void get_new(char * from,char * to)/*复制sigaction数据从fs数据段的from处到内核数据段的to处。*/
{
	int i;

	for (i=0 ; i< sizeof(struct sigaction) ; i++)
		*(to++) = get_fs_byte(from++);
}

int sys_signal(int signum, long handler, long restorer)/*参数1：需捕获的信号，参数2：新的信号处理函数指针。为信号是参数1的信号安装一个新的信号处理程序。*/
{
	struct sigaction tmp;

	if (signum<1 || signum>32 || signum==SIGKILL)/*信号需在（1－32）间，且不能为SIGKILL和SIGSTOP（这两个信号不能被进程捕获）*/
		return -1;
	tmp.sa_handler = (void (*)(int)) handler;
	tmp.sa_mask = 0;
	tmp.sa_flags = SA_ONESHOT | SA_NOMASK;
	tmp.sa_restorer = (void (*)(void)) restorer;
	handler = (long) current->sigaction[signum-1].sa_handler;
	current->sigaction[signum-1] = tmp;
	return handler;
}

int sys_sigaction(int signum, const struct sigaction * action,/*设置用户自定义的信号处理程序*/
	struct sigaction * oldaction)
{
	struct sigaction tmp;

	if (signum<1 || signum>32 || signum==SIGKILL)
		return -1;
	tmp = current->sigaction[signum-1];
	get_new((char *) action,
		(char *) (signum-1+current->sigaction));
	if (oldaction)
		save_old((char *) &tmp,(char *) oldaction);
	if (current->sigaction[signum-1].sa_flags & SA_NOMASK)
		current->sigaction[signum-1].sa_mask = 0;
	else
		current->sigaction[signum-1].sa_mask |= (1<<(signum-1));
	return 0;
}

void do_signal(long signr,long eax, long ebx, long ecx, long edx,/*信号预处理程序（system_call，119）,将iret返回地址设为用户自定义的信号处理程序的入口地址*/
	long fs, long es, long ds,
	long eip, long cs, long eflags,
	unsigned long * esp, long ss)
{                                       /*p211*/
	unsigned long sa_handler;
	long old_eip=eip;
	struct sigaction * sa = current->sigaction + signr - 1;
	int longs;
	unsigned long * tmp_esp;

	sa_handler = (unsigned long) sa->sa_handler;
	if (sa_handler==1)  /*无视信号*/
		return;
	if (!sa_handler) {
		if (signr==SIGCHLD)
			return;
		else
			do_exit(1<<(signr-1));  /*默认信号处理*/
	}
	if (sa->sa_flags & SA_ONESHOT)
		sa->sa_handler = NULL;
	*(&eip) = sa_handler;    /*自定义信号处理*/
	longs = (sa->sa_flags & SA_NOMASK)?7:8;
	*(&esp) -= longs;
	verify_area(esp,longs*4);
	tmp_esp=esp;
	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;
}