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realemu: handle address overflow

--- a/sys/src/cmd/aux/realemu/xec.c

+++ b/sys/src/cmd/aux/realemu/xec.c

@@ -15,6 +15,7 @@

 	p = amem(sp->cpu, a->len, RSS, ar(sp));

 	p->off -= a->len;

+	p->off &= mask(sp->len*8);

 	aw(p, ar(a));

 	aw(sp, p->off);

 }

@@ -495,12 +496,9 @@

 	x = i->a1;

 	s = x->len*8;

 	if(x->tag == TMEM){

-		int z;

-

 		x = adup(x);

 		x->off += (n / s) * x->len;

-		z = i->alen*8;

-		x->off &= mask(z);

+		x->off &= mask(i->alen*8);

 	}

 	a = ar(x);

 	n &= s-1;

@@ -972,9 +970,10 @@

 opmovs(Cpu *cpu, Inst *i)

 {

 	Iarg *cx, *d, *s;

-	ulong c;

+	ulong c, m;

 	int n;

+	m = mask(i->alen*8);

 	d = adup(i->a1);

 	s = adup(i->a2);

 	n = s->len;

@@ -990,7 +989,9 @@

 	while(c){

 		aw(d, ar(s));

 		d->off += n;

+		d->off &= m;

 		s->off += n;

+		s->off &= m;

 		c--;

 	}

 	aw(areg(cpu, i->alen, RDI), d->off);

@@ -1003,9 +1004,10 @@

 oplods(Cpu *cpu, Inst *i)

 {

 	Iarg *cx, *s;

-	ulong c;

+	ulong c, m;

 	int n;

+	m = mask(i->alen*8);

 	s = adup(i->a2);

 	n = s->len;

 	if(cpu->reg[RFL] & DF)

@@ -1019,8 +1021,10 @@

 	}

 	if(c){

 		s->off += n*(c-1);

+		s->off &= m;

 		aw(i->a1, ar(s));

 		s->off += n;

+		s->off &= m;

 	}

 	aw(areg(cpu, i->alen, RSI), s->off);

 	if(cx)

@@ -1031,9 +1035,10 @@

 opstos(Cpu *cpu, Inst *i)

 {

 	Iarg *cx, *d;

-	ulong c, a;

+	ulong c, a, m;

 	int n;

+	m = mask(i->alen*8);

 	d = adup(i->a1);

 	n = d->len;

 	if(cpu->reg[RFL] & DF)

@@ -1049,6 +1054,7 @@

 	while(c){

 		aw(d, a);

 		d->off += n;

+		d->off &= m;

 		c--;

 	}

 	aw(areg(cpu, i->alen, RDI), d->off);

@@ -1059,26 +1065,25 @@

 static int

 repcond(Cpu *cpu, int rep)

 {

-	switch(rep){

-	case OREPNE:

+	if(rep == OREPNE)

 		return (cpu->reg[RFL] & ZF) == 0;

-	case OREPE:

-	default:

-		return !rep || (cpu->reg[RFL] & ZF) != 0;

-	}

+	return !rep || (cpu->reg[RFL] & ZF) != 0;

 }

 static void

 opscas(Cpu *cpu, Inst *i)

 {

-	Iarg *cx, *s;

-	ulong c;

+	Iarg *cx, *d;

+	ulong *f, c, m;

 	long a;

-	int n;

+	int n, z;

-	s = adup(i->a1);

-	n = s->len;

-	if(cpu->reg[RFL] & DF)

+	m = mask(i->alen*8);

+	d = adup(i->a1);

+	n = d->len;

+	z = n*8;

+	f = cpu->reg + RFL;

+	if(*f & DF)

 		n = -n;

 	if(i->rep){

 		cx = areg(cpu, i->alen, RCX);

@@ -1089,13 +1094,14 @@

 	}

 	a = ars(i->a2);

 	while(c){

-		sub(cpu->reg + RFL, a, ars(s), 0, s->len*8);

-		s->off += n;

+		sub(f, a, ars(d), 0, z);

+		d->off += n;

+		d->off &= m;

 		c--;

 		if(repcond(cpu, i->rep))

 			break;

 	}

-	aw(areg(cpu, i->alen, RDI), s->off);

+	aw(areg(cpu, i->alen, RDI), d->off);

 	if(cx)

 		aw(cx, c);

 }

@@ -1104,13 +1110,16 @@

 opcmps(Cpu *cpu, Inst *i)

 {

 	Iarg *cx, *s, *d;

-	ulong c;

-	int n;

+	ulong *f, c, m;

+	int n, z;

+	m = mask(i->alen*8);

 	d = adup(i->a1);

 	s = adup(i->a2);

 	n = s->len;

-	if(cpu->reg[RFL] & DF)

+	z = n*8;

+	f = cpu->reg + RFL;

+	if(*f & DF)

 		n = -n;

 	if(i->rep){

 		cx = areg(cpu, i->alen, RCX);

@@ -1120,9 +1129,11 @@

 		c = 1;

 	}

 	while(c){

-		sub(cpu->reg + RFL, ars(s), ars(d), 0, s->len*8);

+		sub(f, ars(s), ars(d), 0, z);

 		s->off += n;

+		s->off &= m;

 		d->off += n;

+		d->off &= m;

 		c--;

 		if(repcond(cpu, i->rep))

 			break;

-- 

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