signal.c

linux操作系统1.0版本

/*
 *  linux/kernel/signal.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/errno.h>
#include <linux/wait.h>
#include <linux/ptrace.h>
#include <linux/unistd.h>

#include <asm/segment.h>

#define _S(nr) (1<<((nr)-1))

#define _BLOCKABLE (~(_S(SIGKILL) | _S(SIGSTOP)))

extern int core_dump(long signr,struct pt_regs * regs);

asmlinkage int do_signal(unsigned long oldmask, struct pt_regs * regs);

struct sigcontext_struct {
	unsigned short gs, __gsh;
	unsigned short fs, __fsh;
	unsigned short es, __esh;
	unsigned short ds, __dsh;
	unsigned long edi;
	unsigned long esi;
	unsigned long ebp;
	unsigned long esp;
	unsigned long ebx;
	unsigned long edx;
	unsigned long ecx;
	unsigned long eax;
	unsigned long trapno;
	unsigned long err;
	unsigned long eip;
	unsigned short cs, __csh;
	unsigned long eflags;
	unsigned long esp_at_signal;
	unsigned short ss, __ssh;
	unsigned long i387;
	unsigned long oldmask;
	unsigned long cr2;
};

asmlinkage int sys_sigprocmask(int how, sigset_t *set, sigset_t *oset)
{
	sigset_t new_set, old_set = current->blocked;
	int error;

	if (set) {
		error = verify_area(VERIFY_READ, set, sizeof(sigset_t));
		if (error)
			return error;
		new_set = get_fs_long((unsigned long *) set) & _BLOCKABLE;
		switch (how) {
		case SIG_BLOCK:
			current->blocked |= new_set;
			break;
		case SIG_UNBLOCK:
			current->blocked &= ~new_set;
			break;
		case SIG_SETMASK:
			current->blocked = new_set;
			break;
		default:
			return -EINVAL;
		}
	}
	if (oset) {
		error = verify_area(VERIFY_WRITE, oset, sizeof(sigset_t));
		if (error)
			return error;
		put_fs_long(old_set, (unsigned long *) oset);
	}
	return 0;
}

asmlinkage int sys_sgetmask(void)
{
	return current->blocked;
}

asmlinkage int sys_ssetmask(int newmask)
{
	int old=current->blocked;

	current->blocked = newmask & _BLOCKABLE;
	return old;
}

asmlinkage int sys_sigpending(sigset_t *set)
{
	int error;
	/* fill in "set" with signals pending but blocked. */
	error = verify_area(VERIFY_WRITE, set, 4);
	if (!error)
		put_fs_long(current->blocked & current->signal, (unsigned long *)set);
	return error;
}

/*
 * atomically swap in the new signal mask, and wait for a signal.
 */
asmlinkage int sys_sigsuspend(int restart, unsigned long oldmask, unsigned long set)
{
	unsigned long mask;
	struct pt_regs * regs = (struct pt_regs *) &restart;

	mask = current->blocked;
	current->blocked = set & _BLOCKABLE;
	regs->eax = -EINTR;
	while (1) {
		current->state = TASK_INTERRUPTIBLE;
		schedule();
		if (do_signal(mask,regs))
			return -EINTR;
	}
}

/*
 * POSIX 3.3.1.3:
 *  "Setting a signal action to SIG_IGN for a signal that is pending
 *   shall cause the pending signal to be discarded, whether or not
 *   it is blocked" (but SIGCHLD is unspecified: linux leaves it alone).
 *
 *  "Setting a signal action to SIG_DFL for a signal that is pending
 *   and whose default action is to ignore the signal (for example,
 *   SIGCHLD), shall cause the pending signal to be discarded, whether
 *   or not it is blocked"
 *
 * Note the silly behaviour of SIGCHLD: SIG_IGN means that the signal
 * isn't actually ignored, but does automatic child reaping, while
 * SIG_DFL is explicitly said by POSIX to force the signal to be ignored..
 */
static void check_pending(int signum)
{
	struct sigaction *p;

	p = signum - 1 + current->sigaction;
	if (p->sa_handler == SIG_IGN) {
		if (signum == SIGCHLD)
			return;
		current->signal &= ~_S(signum);
		return;
	}
	if (p->sa_handler == SIG_DFL) {
		if (signum != SIGCONT && signum != SIGCHLD && signum != SIGWINCH)
			return;
		current->signal &= ~_S(signum);
		return;
	}	
}

asmlinkage int sys_signal(int signum, unsigned long handler)
{
	struct sigaction tmp;

	if (signum<1 || signum>32 || signum==SIGKILL || signum==SIGSTOP)
		return -EINVAL;
	if (handler >= TASK_SIZE)
		return -EFAULT;
	tmp.sa_handler = (void (*)(int)) handler;
	tmp.sa_mask = 0;
	tmp.sa_flags = SA_ONESHOT | SA_NOMASK;
	tmp.sa_restorer = NULL;
	handler = (long) current->sigaction[signum-1].sa_handler;
	current->sigaction[signum-1] = tmp;
	check_pending(signum);
	return handler;
}

asmlinkage int sys_sigaction(int signum, const struct sigaction * action,
	struct sigaction * oldaction)
{
	struct sigaction new_sa, *p;

	if (signum<1 || signum>32 || signum==SIGKILL || signum==SIGSTOP)
		return -EINVAL;
	p = signum - 1 + current->sigaction;
	if (action) {
		int err = verify_area(VERIFY_READ, action, sizeof(*action));
		if (err)
			return err;
		memcpy_fromfs(&new_sa, action, sizeof(struct sigaction));
		if (new_sa.sa_flags & SA_NOMASK)
			new_sa.sa_mask = 0;
		else {
			new_sa.sa_mask |= _S(signum);
			new_sa.sa_mask &= _BLOCKABLE;
		}
		if (TASK_SIZE <= (unsigned long) new_sa.sa_handler)
			return -EFAULT;
	}
	if (oldaction) {
		int err = verify_area(VERIFY_WRITE, oldaction, sizeof(*oldaction));
		if (err)
			return err;
		memcpy_tofs(oldaction, p, sizeof(struct sigaction));
	}
	if (action) {
		*p = new_sa;
		check_pending(signum);
	}
	return 0;
}

asmlinkage int sys_waitpid(pid_t pid,unsigned long * stat_addr, int options);

/*
 * This sets regs->esp even though we don't actually use sigstacks yet..
 */
asmlinkage int sys_sigreturn(unsigned long __unused)
{
#define COPY(x) regs->x = context.x
#define COPY_SEG(x) \
if ((context.x & 0xfffc) && (context.x & 3) != 3) goto badframe; COPY(x);
#define COPY_SEG_STRICT(x) \
if (!(context.x & 0xfffc) || (context.x & 3) != 3) goto badframe; COPY(x);
	struct sigcontext_struct context;
	struct pt_regs * regs;

	regs = (struct pt_regs *) &__unused;
	if (verify_area(VERIFY_READ, (void *) regs->esp, sizeof(context)))
		goto badframe;
	memcpy_fromfs(&context,(void *) regs->esp, sizeof(context));
	current->blocked = context.oldmask & _BLOCKABLE;
	COPY_SEG(ds);
	COPY_SEG(es);
	COPY_SEG(fs);
	COPY_SEG(gs);
	COPY_SEG_STRICT(ss);
	COPY_SEG_STRICT(cs);
	COPY(eip);
	COPY(ecx); COPY(edx);
	COPY(ebx);
	COPY(esp); COPY(ebp);
	COPY(edi); COPY(esi);
	regs->eflags &= ~0xCD5;
	regs->eflags |= context.eflags & 0xCD5;
	regs->orig_eax = -1;		/* disable syscall checks */
	return context.eax;
badframe:
	do_exit(SIGSEGV);
}

/*
 * Set up a signal frame... Make the stack look the way iBCS2 expects
 * it to look.
 */
static void setup_frame(struct sigaction * sa, unsigned long ** fp, unsigned long eip,
	struct pt_regs * regs, int signr, unsigned long oldmask)
{
	unsigned long * frame;

#define __CODE ((unsigned long)(frame+24))
#define CODE(x) ((unsigned long *) ((x)+__CODE))
	frame = *fp;
	if (regs->ss != USER_DS)
		frame = (unsigned long *) sa->sa_restorer;
	frame -= 32;
	if (verify_area(VERIFY_WRITE,frame,32*4))
		do_exit(SIGSEGV);
/* set up the "normal" stack seen by the signal handler (iBCS2) */
	put_fs_long(__CODE,frame);
	put_fs_long(signr, frame+1);
	put_fs_long(regs->gs, frame+2);
	put_fs_long(regs->fs, frame+3);
	put_fs_long(regs->es, frame+4);
	put_fs_long(regs->ds, frame+5);
	put_fs_long(regs->edi, frame+6);
	put_fs_long(regs->esi, frame+7);
	put_fs_long(regs->ebp, frame+8);
	put_fs_long((long)*fp, frame+9);
	put_fs_long(regs->ebx, frame+10);
	put_fs_long(regs->edx, frame+11);
	put_fs_long(regs->ecx, frame+12);
	put_fs_long(regs->eax, frame+13);
	put_fs_long(current->tss.trap_no, frame+14);
	put_fs_long(current->tss.error_code, frame+15);
	put_fs_long(eip, frame+16);
	put_fs_long(regs->cs, frame+17);
	put_fs_long(regs->eflags, frame+18);
	put_fs_long(regs->esp, frame+19);
	put_fs_long(regs->ss, frame+20);
	put_fs_long(0,frame+21);		/* 387 state pointer - not implemented*/
/* non-iBCS2 extensions.. */
	put_fs_long(oldmask, frame+22);
	put_fs_long(current->tss.cr2, frame+23);
/* set up the return code... */
	put_fs_long(0x0000b858, CODE(0));	/* popl %eax ; movl $,%eax */
	put_fs_long(0x80cd0000, CODE(4));	/* int $0x80 */
	put_fs_long(__NR_sigreturn, CODE(2));
	*fp = frame;
#undef __CODE
#undef CODE
}

/*
 * Note that 'init' is a special process: it doesn't get signals it doesn't
 * want to handle. Thus you cannot kill init even with a SIGKILL even by
 * mistake.
 *
 * Note that we go through the signals twice: once to check the signals that
 * the kernel can handle, and then we build all the user-level signal handling
 * stack-frames in one go after that.
 */
asmlinkage int do_signal(unsigned long oldmask, struct pt_regs * regs)
{
	unsigned long mask = ~current->blocked;
	unsigned long handler_signal = 0;
	unsigned long *frame = NULL;
	unsigned long eip = 0;
	unsigned long signr;
	struct sigaction * sa;

	while ((signr = current->signal & mask)) {
		__asm__("bsf %2,%1\n\t"
			"btrl %1,%0"
			:"=m" (current->signal),"=r" (signr)
			:"1" (signr));
		sa = current->sigaction + signr;
		signr++;
		if ((current->flags & PF_PTRACED) && signr != SIGKILL) {
			current->exit_code = signr;
			current->state = TASK_STOPPED;
			notify_parent(current);
			schedule();
			if (!(signr = current->exit_code))
				continue;
			current->exit_code = 0;
			if (signr == SIGSTOP)
				continue;
			if (_S(signr) & current->blocked) {
				current->signal |= _S(signr);
				continue;
			}
			sa = current->sigaction + signr - 1;
		}
		if (sa->sa_handler == SIG_IGN) {
			if (signr != SIGCHLD)
				continue;
			/* check for SIGCHLD: it's special */
			while (sys_waitpid(-1,NULL,WNOHANG) > 0)
				/* nothing */;
			continue;
		}
		if (sa->sa_handler == SIG_DFL) {
			if (current->pid == 1)
				continue;
			switch (signr) {
			case SIGCONT: case SIGCHLD: case SIGWINCH:
				continue;

			case SIGSTOP: case SIGTSTP: case SIGTTIN: case SIGTTOU:
				if (current->flags & PF_PTRACED)
					continue;
				current->state = TASK_STOPPED;
				current->exit_code = signr;
				if (!(current->p_pptr->sigaction[SIGCHLD-1].sa_flags & 
						SA_NOCLDSTOP))
					notify_parent(current);
				schedule();
				continue;

			case SIGQUIT: case SIGILL: case SIGTRAP:
			case SIGIOT: case SIGFPE: case SIGSEGV:
				if (core_dump(signr,regs))
					signr |= 0x80;
				/* fall through */
			default:
				current->signal |= _S(signr & 0x7f);
				do_exit(signr);
			}
		}
		/*
		 * OK, we're invoking a handler
		 */
		if (regs->orig_eax >= 0) {
			if (regs->eax == -ERESTARTNOHAND ||
			   (regs->eax == -ERESTARTSYS && !(sa->sa_flags & SA_RESTART)))
				regs->eax = -EINTR;
		}
		handler_signal |= 1 << (signr-1);
		mask &= ~sa->sa_mask;
	}
	if (regs->orig_eax >= 0 &&
	    (regs->eax == -ERESTARTNOHAND ||
	     regs->eax == -ERESTARTSYS ||
	     regs->eax == -ERESTARTNOINTR)) {
		regs->eax = regs->orig_eax;
		regs->eip -= 2;
	}
	if (!handler_signal)		/* no handler will be called - return 0 */
		return 0;
	eip = regs->eip;
	frame = (unsigned long *) regs->esp;
	signr = 1;
	sa = current->sigaction;
	for (mask = 1 ; mask ; sa++,signr++,mask += mask) {
		if (mask > handler_signal)
			break;
		if (!(mask & handler_signal))
			continue;
		setup_frame(sa,&frame,eip,regs,signr,oldmask);
		eip = (unsigned long) sa->sa_handler;
		if (sa->sa_flags & SA_ONESHOT)
			sa->sa_handler = NULL;
/* force a supervisor-mode page-in of the signal handler to reduce races */
		__asm__("testb $0,%%fs:%0": :"m" (*(char *) eip));
		regs->cs = USER_CS; regs->ss = USER_DS;
		regs->ds = USER_DS; regs->es = USER_DS;
		regs->gs = USER_DS; regs->fs = USER_DS;
		current->blocked |= sa->sa_mask;
		oldmask |= sa->sa_mask;
	}
	regs->esp = (unsigned long) frame;
	regs->eip = eip;		/* "return" to the first handler */
	current->tss.trap_no = current->tss.error_code = 0;
	return 1;
}