trap.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

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/*
 * Fill in enough of Ureg to get a stack trace, and call a function.
 * Used by debugging interface rdb.
 */

static void
getpcsp(ulong *pc, ulong *sp)
{
	*pc = getcallerpc(&pc);
	*sp = (ulong)&pc-4;
}

void
callwithureg(void (*fn)(Ureg*))
{
	Ureg ureg;

	getpcsp((ulong*)&ureg.pc, (ulong*)&ureg.sp);
	ureg.lr = getcallerpc(&fn);
	fn(&ureg);
}

static void
_dumpstack(Ureg *ureg)
{
	ulong l, sl, el, v;
	int i;

	l = (ulong)&l;
	if(up == 0){
		el = (ulong)m+BY2PG;
		sl = el-KSTACK;
	}
	else{
		sl = (ulong)up->kstack;
		el = sl + KSTACK;
	}
	if(l > el || l < sl){
		el = (ulong)m+BY2PG;
		sl = el-KSTACK;
	}
	if(l > el || l < sl)
		return;
	print("ktrace /kernel/path %.8lux %.8lux %.8lux\n", ureg->pc, ureg->sp, ureg->lr);
	i = 0;
	for(; l < el; l += 4){
		v = *(ulong*)l;
		if(KTZERO < v && v < (ulong)etext){
			print("%.8lux=%.8lux ", l, v);
			if(i++ == 4){
				print("\n");
				i = 0;
			}
		}
	}
}

void
dumpstack(void)
{
	callwithureg(_dumpstack);
}

void
dumpregs(Ureg *ur)
{
	int i;
	ulong *l;

	if(up) {
		print("registers for %s %ld\n", up->text, up->pid);
		if(ur->srr1 & MSR_PR == 0)
		if(ur->usp < (ulong)up->kstack || ur->usp > (ulong)up->kstack+KSTACK)
			print("invalid stack ptr\n");
	}
	else
		print("registers for kernel\n");

	print("dsisr\t%.8lux\tdar\t%.8lux\n", getdsisr(), getdar());
	l = &ur->cause;
	for(i=0; i<sizeof regname/sizeof(char*); i+=2, l+=2)
		print("%s\t%.8lux\t%s\t%.8lux\n", regname[i], l[0], regname[i+1], l[1]);
}

static void
linkproc(void)
{
	spllo();
	(*up->kpfun)(up->kparg);
	pexit("", 0);
}

void
kprocchild(Proc *p, void (*func)(void*), void *arg)
{
	p->sched.pc = (ulong)linkproc;
	p->sched.sp = (ulong)p->kstack+KSTACK;

	p->kpfun = func;
	p->kparg = arg;
}

/*
 * called in sysfile.c
 */
void
evenaddr(ulong addr)
{
	if(addr & 3){
		postnote(up, 1, "sys: odd address", NDebug);
		error(Ebadarg);
	}
}

long
execregs(ulong entry, ulong ssize, ulong nargs)
{
	ulong *sp;
	Ureg *ureg;

	sp = (ulong*)(USTKTOP - ssize);
	*--sp = nargs;

	ureg = up->dbgreg;
	ureg->usp = (ulong)sp;
	ureg->pc = entry;
	ureg->srr1 &= ~MSR_FP;
	return USTKTOP-sizeof(Tos);		/* address of kernel/user shared data */
}

void
forkchild(Proc *p, Ureg *ur)
{
	Ureg *cur;

	p->sched.sp = (ulong)p->kstack+KSTACK-UREGSIZE;
	p->sched.pc = (ulong)forkret;

	cur = (Ureg*)(p->sched.sp+2*BY2WD);
	memmove(cur, ur, sizeof(Ureg));
	cur->r3 = 0;
	
	/* Things from bottom of syscall we never got to execute */
	p->psstate = 0;
	p->insyscall = 0;
}

ulong
userpc(void)
{
	Ureg *ureg;

	ureg = (Ureg*)up->dbgreg;
	return ureg->pc;
}


/* This routine must save the values of registers the user is not 
 * permitted to write from devproc and then restore the saved values 
 * before returning
 */
void
setregisters(Ureg *xp, char *pureg, char *uva, int n)
{
	ulong status;

	status = xp->status;
	memmove(pureg, uva, n);
	xp->status = status;
}

/* Give enough context in the ureg to produce a kernel stack for
 * a sleeping process
 */
void
setkernur(Ureg* ureg, Proc* p)
{
	ureg->pc = p->sched.pc;
	ureg->sp = p->sched.sp+4;
}

ulong
dbgpc(Proc *p)
{
	Ureg *ureg;

	ureg = p->dbgreg;
	if(ureg == 0)
		return 0;

	return ureg->pc;
}

/*
 *  system calls
 */
#include "../port/systab.h"

/* TODO: make this trap a separate asm entry point, like on other RISC architectures */
void
syscall(Ureg* ureg)
{
	int i;
	char *e;
	long	ret;
	ulong sp, scallnr;

	m->syscall++;
	up->insyscall = 1;
	up->pc = ureg->pc;
	up->dbgreg = ureg;

	scallnr = ureg->r3;
	up->scallnr = ureg->r3;
	spllo();

	sp = ureg->usp;
	up->nerrlab = 0;
	ret = -1;
	if(!waserror()){
		if(scallnr >= nsyscall || systab[scallnr] == nil){
			pprint("bad sys call number %d pc %lux\n", scallnr, ureg->pc);
			postnote(up, 1, "sys: bad sys call", NDebug);
			error(Ebadarg);
		}

		if(sp<(USTKTOP-BY2PG) || sp>(USTKTOP-sizeof(Sargs)-BY2WD))
			validaddr(sp, sizeof(Sargs)+BY2WD, 0);

		up->s = *((Sargs*)(sp+BY2WD));
		up->psstate = sysctab[scallnr];

		ret = systab[scallnr](up->s.args);
		poperror();
	}else{
		/* failure: save the error buffer for errstr */
		e = up->syserrstr;
		up->syserrstr = up->errstr;
		up->errstr = e;
	}
	if(up->nerrlab){
		print("bad errstack [%uld]: %d extra\n", scallnr, up->nerrlab);
		print("scall %s lr =%lux\n", sysctab[scallnr], ureg->lr);
		for(i = 0; i < NERR; i++)
			print("sp=%lux pc=%lux\n", up->errlab[i].sp, up->errlab[i].pc);
		panic("error stack");
	}

	up->insyscall = 0;
	up->psstate = 0;

	/*
	 *  Put return value in frame.  On the x86 the syscall is
	 *  just another trap and the return value from syscall is
	 *  ignored.  On other machines the return value is put into
	 *  the results register by caller of syscall.
	 */
	ureg->r3 = ret;

	if(scallnr == NOTED)
		noted(ureg, *(ulong*)(sp+BY2WD));

	/* restoreureg must execute at high IPL */
	splhi();
	if(scallnr!=RFORK)
		notify(ureg);
	if(up->fpstate == FPinactive)
		ureg->srr1 &= ~MSR_FP;
}

/*
 *  Call user, if necessary, with note.
 *  Pass user the Ureg struct and the note on his stack.
 */
int
notify(Ureg* ur)
{
	int l;
	ulong s, sp;
	Note *n;

	if(up->procctl)
		procctl(up);
	if(up->nnote == 0)
		return 0;

	s = spllo();
	qlock(&up->debug);
	up->notepending = 0;
	n = &up->note[0];
	if(strncmp(n->msg, "sys:", 4) == 0){
		l = strlen(n->msg);
		if(l > ERRMAX-15)	/* " pc=0x12345678\0" */
			l = ERRMAX-15;
		sprint(n->msg+l, " pc=0x%.8lux", ur->pc);
	}

	if(n->flag!=NUser && (up->notified || up->notify==0)){
		if(n->flag == NDebug)
			pprint("suicide: %s\n", n->msg);
		qunlock(&up->debug);
		pexit(n->msg, n->flag!=NDebug);
	}

	if(up->notified) {
		qunlock(&up->debug);
		splhi();
		return 0;
	}

	if(!up->notify) {
		qunlock(&up->debug);
		pexit(n->msg, n->flag!=NDebug);
	}
	sp = ur->usp & ~(BY2V-1);
	sp -= sizeof(Ureg);

	if(!okaddr((ulong)up->notify, BY2WD, 0) ||
	   !okaddr(sp-ERRMAX-4*BY2WD, sizeof(Ureg)+ERRMAX+4*BY2WD, 1)) {
		pprint("suicide: bad address or sp in notify\n");
		qunlock(&up->debug);
		pexit("Suicide", 0);
	}

	memmove((Ureg*)sp, ur, sizeof(Ureg));
	*(Ureg**)(sp-BY2WD) = up->ureg;	/* word under Ureg is old up->ureg */
	up->ureg = (void*)sp;
	sp -= BY2WD+ERRMAX;
	memmove((char*)sp, up->note[0].msg, ERRMAX);
	sp -= 3*BY2WD;
	*(ulong*)(sp+2*BY2WD) = sp+3*BY2WD;	/* arg 2 is string */
	ur->r1 = (long)up->ureg;		/* arg 1 is ureg* */
	((ulong*)sp)[1] = (ulong)up->ureg;	/* arg 1 0(FP) is ureg* */
	((ulong*)sp)[0] = 0;			/* arg 0 is pc */
	ur->usp = sp;
	ur->pc = (ulong)up->notify;
	up->notified = 1;
	up->nnote--;
	memmove(&up->lastnote, &up->note[0], sizeof(Note));
	memmove(&up->note[0], &up->note[1], up->nnote*sizeof(Note));

	qunlock(&up->debug);
	splx(s);
	return 1;
}


/*
 *   Return user to state before notify()
 */
void
noted(Ureg* ureg, ulong arg0)
{
	Ureg *nureg;
	ulong oureg, sp;

	qlock(&up->debug);
	if(arg0!=NRSTR && !up->notified) {
		qunlock(&up->debug);
		pprint("call to noted() when not notified\n");
		pexit("Suicide", 0);
	}
	up->notified = 0;

	nureg = up->ureg;	/* pointer to user returned Ureg struct */

	/* sanity clause */
	oureg = (ulong)nureg;
	if(!okaddr((ulong)oureg-BY2WD, BY2WD+sizeof(Ureg), 0)){
		pprint("bad ureg in noted or call to noted when not notified\n");
		qunlock(&up->debug);
		pexit("Suicide", 0);
	}

	memmove(ureg, nureg, sizeof(Ureg));

	switch(arg0){
	case NCONT:
	case NRSTR:
		if(!okaddr(nureg->pc, 1, 0) || !okaddr(nureg->usp, BY2WD, 0)){
			pprint("suicide: trap in noted\n");
			qunlock(&up->debug);
			pexit("Suicide", 0);
		}
		up->ureg = (Ureg*)(*(ulong*)(oureg-BY2WD));
		qunlock(&up->debug);
		break;

	case NSAVE:
		if(!okaddr(nureg->pc, BY2WD, 0)
		|| !okaddr(nureg->usp, BY2WD, 0)){
			pprint("suicide: trap in noted\n");
			qunlock(&up->debug);
			pexit("Suicide", 0);
		}
		qunlock(&up->debug);
		sp = oureg-4*BY2WD-ERRMAX;
		splhi();
		ureg->sp = sp;
		((ulong*)sp)[1] = oureg;	/* arg 1 0(FP) is ureg* */
		((ulong*)sp)[0] = 0;		/* arg 0 is pc */
		break;

	default:
		pprint("unknown noted arg 0x%lux\n", arg0);
		up->lastnote.flag = NDebug;
		/* fall through */
		
	case NDFLT:
		if(up->lastnote.flag == NDebug)
			pprint("suicide: %s\n", up->lastnote.msg);
		qunlock(&up->debug);
		pexit(up->lastnote.msg, up->lastnote.flag!=NDebug);
	}
}