5l, 8l: pass stack frame size to morestack when needed

Shame on me: I fixed the same bug in 6l in 8691fcc6a66e
(https://golang.org/cl/2609041) and neglected
to look at 5l and 8l to see if they were affected.

On the positive side, the check I added in that CL is the
one that detected this bug.

Fixes #1457.

R=ken2
CC=golang-dev
https://golang.org/cl/3981052

src/cmd/5l/noop.c

@@ -330,13 +330,14 @@ noops(void)
 						p->from.reg = 1;
 						p->reg = 2;
 					}
-	
+
 					// MOVW.LO		$autosize, R1
 					p = appendp(p);
 					p->as = AMOVW;
 					p->scond = C_SCOND_LO;
 					p->from.type = D_CONST;
-					p->from.offset = 0;
+					/* 160 comes from 3 calls (3*8) 4 safes (4*8) and 104 guard */
+					p->from.offset = autosize+160;
 					p->to.type = D_REG;
 					p->to.reg = 1;
 	

src/cmd/8l/pass.c

@@ -517,7 +517,7 @@ dostkoff(void)
 			p->to.type = D_DX;
 			/* 160 comes from 3 calls (3*8) 4 safes (4*8) and 104 guard */
 			p->from.type = D_CONST;
-			if(autoffset+160 > 4096)
+			if(autoffset+160+cursym->text->to.offset2 > 4096)
 				p->from.offset = (autoffset+160) & ~7LL;
 
 			p = appendp(p);	// save arg size in AX

src/pkg/runtime/proc.c

@@ -723,8 +723,10 @@ runtime·newstack(void)
 	argsize = m->moreargsize;
 	g1 = m->curg;
 
-	if(m->morebuf.sp < g1->stackguard - StackGuard)
-		runtime·throw("split stack overflow");
+	if(m->morebuf.sp < g1->stackguard - StackGuard) {
+		runtime·printf("runtime: split stack overflow: %p < %p\n", m->morebuf.sp, g1->stackguard - StackGuard);
+		runtime·throw("runtime: split stack overflow");
+	}
 
 	reflectcall = framesize==1;
 	if(reflectcall)

test/stack.go

@@ -30,6 +30,32 @@ func d(t T) {
 	}
 }
 
+func f0() {
+	// likely to make a new stack for f0,
+	// because the call to f1 puts 3000 bytes
+	// in our frame.
+	f1()
+}
+
+func f1() [3000]byte {
+	// likely to make a new stack for f1,
+	// because 3000 bytes were used by f0
+	// and we need 3000 more for the call
+	// to f2.  if the call to morestack in f1
+	// does not pass the frame size, the new
+	// stack (default size 5k) will not be big
+	// enough for the frame, and the morestack
+	// check in f2 will die, if we get that far 
+	// without faulting.
+	f2()
+	return [3000]byte{}
+}
+
+func f2() [3000]byte {
+	// just take up space
+	return [3000]byte{}
+}
+
 var c = make(chan int)
 var t T
 var b = []byte{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
@@ -40,6 +66,7 @@ func recur(n int) {
 		panic("bad []byte -> string")
 	}
 	go g(c, t)
+	f0()
 	s := <-c
 	if s != len(t) {
 		println("bad go", s)