cmd/gc: implement latest rules for checking make sizes

Fixes #4085.

R=ken2
CC=golang-dev
https://golang.org/cl/7277047

src/cmd/gc/mparith1.c

@@ -43,10 +43,10 @@ mpcmpfixfix(Mpint *a, Mpint *b)
 int
 mpcmpfixc(Mpint *b, vlong c)
 {
-	Mpint a;
+	Mpint c1;
 
-	mpmovecfix(&a, c);
-	return mpcmpfixfix(&a, b);
+	mpmovecfix(&c1, c);
+	return mpcmpfixfix(b, &c1);
 }
 
 int

src/cmd/gc/typecheck.c

@@ -32,6 +32,7 @@ static void	checkassignlist(NodeList*);
 static void	stringtoarraylit(Node**);
 static Node*	resolve(Node*);
 static void	checkdefergo(Node*);
+static int	checkmake(Type*, char*, Node*);
 
 static	NodeList*	typecheckdefstack;
 
@@ -1403,22 +1404,20 @@ reswitch:
 			l = args->n;
 			args = args->next;
 			typecheck(&l, Erv);
-			defaultlit(&l, types[TINT]);
 			r = N;
 			if(args != nil) {
 				r = args->n;
 				args = args->next;
 				typecheck(&r, Erv);
-				defaultlit(&r, types[TINT]);
 			}
 			if(l->type == T || (r && r->type == T))
 				goto error;
-			if(!isint[l->type->etype]) {
-				yyerror("non-integer len argument to make(%T)", t);
+			et = checkmake(t, "len", l) < 0;
+			et |= r && checkmake(t, "cap", r) < 0;
+			if(et)
 				goto error;
-			}
-			if(r && !isint[r->type->etype]) {
-				yyerror("non-integer cap argument to make(%T)", t);
+			if(isconst(l, CTINT) && r && isconst(r, CTINT) && mpcmpfixfix(l->val.u.xval, r->val.u.xval) > 0) {
+				yyerror("len larger than cap in make(%T)", t);
 				goto error;
 			}
 			n->left = l;
@@ -1434,10 +1433,8 @@ reswitch:
 				defaultlit(&l, types[TINT]);
 				if(l->type == T)
 					goto error;
-				if(!isint[l->type->etype]) {
-					yyerror("non-integer size argument to make(%T)", t);
+				if(checkmake(t, "size", l) < 0)
 					goto error;
-				}
 				n->left = l;
 			} else
 				n->left = nodintconst(0);
@@ -1453,10 +1450,8 @@ reswitch:
 				defaultlit(&l, types[TINT]);
 				if(l->type == T)
 					goto error;
-				if(!isint[l->type->etype]) {
-					yyerror("non-integer buffer argument to make(%T)", t);
+				if(checkmake(t, "buffer", l) < 0)
 					goto error;
-				}
 				n->left = l;
 			} else
 				n->left = nodintconst(0);
@@ -3098,3 +3093,33 @@ ret:
 	n->walkdef = 1;
 	return n;
 }
+
+static int
+checkmake(Type *t, char *arg, Node *n)
+{
+	if(n->op == OLITERAL) {
+		n->val = toint(n->val);
+		if(mpcmpfixc(n->val.u.xval, 0) < 0) {
+			yyerror("negative %s argument in make(%T)", arg, t);
+			return -1;
+		}
+		if(mpcmpfixfix(n->val.u.xval, maxintval[TINT]) > 0) {
+			yyerror("%s argument too large in make(%T)", arg, t);
+			return -1;
+		}
+		
+		// Delay defaultlit until after we've checked range, to avoid
+		// a redundant "constant NNN overflows int" error.
+		defaultlit(&n, types[TINT]);
+		return 0;
+	}
+	
+	// Defaultlit still necessary for non-constant: n might be 1<<k.
+	defaultlit(&n, types[TINT]);
+
+	if(!isint[n->type->etype]) {
+		yyerror("non-integer %s argument in make(%T) - %T", arg, t, n->type);
+		return -1;
+	}
+	return 0;
+}

src/pkg/runtime/slice.c

@@ -20,7 +20,12 @@ static	void	growslice1(SliceType*, Slice, intgo, Slice *);
 void
 runtime·makeslice(SliceType *t, int64 len, int64 cap, Slice ret)
 {
-	if(len < 0 || (intgo)len != len)
+	// NOTE: The len > MaxMem/elemsize check here is not strictly necessary,
+	// but it produces a 'len out of range' error instead of a 'cap out of range' error
+	// when someone does make([]T, bignumber). 'cap out of range' is true too,
+	// but since the cap is only being supplied implicitly, saying len is clearer.
+	// See issue 4085.
+	if(len < 0 || (intgo)len != len || t->elem->size > 0 && len > MaxMem / t->elem->size)
 		runtime·panicstring("makeslice: len out of range");
 
 	if(cap < len || (intgo)cap != cap || t->elem->size > 0 && cap > MaxMem / t->elem->size)

test/fixedbugs/issue4085a.go

+// errorcheck
+
+// Copyright 2013 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+type T []int
+
+func main() {
+	_ = make(T, -1)       // ERROR "negative"
+	_ = make(T, 0.5)       // ERROR "constant 0.5 truncated to integer"
+	_ = make(T, 1.0)       // ok
+	_ = make(T, 1<<63)  // ERROR "len argument too large"
+	_ = make(T, 0, -1)    // ERROR "negative cap"
+	_ = make(T, 10, 0) // ERROR "len larger than cap"
+}

test/fixedbugs/issue4085b.go

+// run
+
+// Copyright 2013 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"strings"
+	"unsafe"
+)
+
+type T []int
+
+func main() {
+	n := -1
+	shouldPanic("len out of range", func() {_ = make(T, n)})
+	shouldPanic("cap out of range", func() {_ = make(T, 0, n)})
+	var t *byte
+	if unsafe.Sizeof(t) == 8 {
+		n = 1<<20
+		n <<= 20
+		shouldPanic("len out of range", func() {_ = make(T, n)})
+		shouldPanic("cap out of range", func() {_ = make(T, 0, n)})
+		n <<= 20
+		shouldPanic("len out of range", func() {_ = make(T, n)})
+		shouldPanic("cap out of range", func() {_ = make(T, 0, n)})
+	} else {
+		n = 1<<31 - 1
+		shouldPanic("len out of range", func() {_ = make(T, n)})
+		shouldPanic("cap out of range", func() {_ = make(T, 0, n)})
+	}
+}
+
+func shouldPanic(str string, f func()) {
+	defer func() {
+		err := recover()
+		if err == nil {
+			panic("did not panic")
+		}
+		s := err.(error).Error()
+		if !strings.Contains(s, str) {
+			panic("got panic " + s + ", want " + str)
+		}
+	}()
+	
+	f()
+}