runtime: introduce cnewarray() to simplify allocation of typed arrays

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/9648044

src/pkg/reflect/all_test.go

@@ -3032,6 +3032,25 @@ func TestSliceOf(t *testing.T) {
 	checkSameType(t, Zero(SliceOf(TypeOf(T1(1)))).Interface(), []T1{})
 }
 
+func TestSliceOverflow(t *testing.T) {
+	// check that MakeSlice panics when size of slice overflows uint
+	const S = 1e6
+	s := uint(S)
+	l := (1<<(unsafe.Sizeof((*byte)(nil))*8)-1)/s + 1
+	if l*s >= s {
+		t.Fatal("slice size does not overflow")
+	}
+	var x [S]byte
+	st := SliceOf(TypeOf(x))
+	defer func() {
+		err := recover()
+		if err == nil {
+			t.Fatal("slice overflow does not panic")
+		}
+	}()
+	MakeSlice(st, int(l), int(l))
+}
+
 func TestSliceOfGC(t *testing.T) {
 	type T *uintptr
 	tt := TypeOf(T(nil))

src/pkg/runtime/iface.c

@@ -687,42 +687,14 @@ reflect·unsafe_Typeof(Eface e, Eface ret)
 void
 reflect·unsafe_New(Type *t, void *ret)
 {
-	uint32 flag;
-
-	flag = t->kind&KindNoPointers ? FlagNoPointers : 0;
-	ret = runtime·mallocgc(t->size, flag, 1, 1);
-
-	if(UseSpanType && !flag) {
-		if(false) {
-			runtime·printf("unsafe_New %S: %p\n", *t->string, ret);
-		}
-		runtime·settype(ret, (uintptr)t | TypeInfo_SingleObject);
-	}
-
+	ret = runtime·cnew(t);
 	FLUSH(&ret);
 }
 
 void
 reflect·unsafe_NewArray(Type *t, intgo n, void *ret)
 {
-	uint64 size;
-
-	size = n*t->size;
-	if(size == 0)
-		ret = (byte*)&runtime·zerobase;
-	else if(t->kind&KindNoPointers)
-		ret = runtime·mallocgc(size, FlagNoPointers, 1, 1);
-	else {
-		ret = runtime·mallocgc(size, 0, 1, 1);
-
-		if(UseSpanType) {
-			if(false) {
-				runtime·printf("unsafe_NewArray [%D]%S: %p\n", (int64)n, *t->string, ret);
-			}
-			runtime·settype(ret, (uintptr)t | TypeInfo_Array);
-		}
-	}
-
+	ret = runtime·cnewarray(t, n);
 	FLUSH(&ret);
 }
 

src/pkg/runtime/malloc.goc

@@ -729,9 +729,8 @@ runtime·new(Type *typ, uint8 *ret)
 		ret = runtime·mallocgc(typ->size, flag, 1, 1);
 
 		if(UseSpanType && !flag) {
-			if(false) {
+			if(false)
 				runtime·printf("new %S: %p\n", *typ->string, ret);
-			}
 			runtime·settype(ret, (uintptr)typ | TypeInfo_SingleObject);
 		}
 	}
@@ -739,36 +738,45 @@ runtime·new(Type *typ, uint8 *ret)
 	FLUSH(&ret);
 }
 
-// same as runtime·new, but callable from C
-void*
-runtime·cnew(Type *typ)
+static void*
+cnew(Type *typ, intgo n, int32 objtyp)
 {
 	uint32 flag;
 	void *ret;
 
-	if(raceenabled)
-		m->racepc = runtime·getcallerpc(&typ);
-
-	if(typ->size == 0) {
+	if((objtyp&(PtrSize-1)) != objtyp)
+		runtime·throw("runtime: invalid objtyp");
+	if(n < 0 || (typ->size > 0 && n > MaxMem/typ->size))
+		runtime·panicstring("runtime: allocation size out of range");
+	if(typ->size == 0 || n == 0) {
 		// All 0-length allocations use this pointer.
 		// The language does not require the allocations to
 		// have distinct values.
-		ret = (uint8*)&runtime·zerobase;
-	} else {
-		flag = typ->kind&KindNoPointers ? FlagNoPointers : 0;
-		ret = runtime·mallocgc(typ->size, flag, 1, 1);
-
-		if(UseSpanType && !flag) {
-			if(false) {
-				runtime·printf("new %S: %p\n", *typ->string, ret);
-			}
-			runtime·settype(ret, (uintptr)typ | TypeInfo_SingleObject);
-		}
+		return &runtime·zerobase;
+	}
+	flag = typ->kind&KindNoPointers ? FlagNoPointers : 0;
+	ret = runtime·mallocgc(typ->size*n, flag, 1, 1);
+	if(UseSpanType && !flag) {
+		if(false)
+			runtime·printf("cnew [%D]%S: %p\n", (int64)n, *typ->string, ret);
+		runtime·settype(ret, (uintptr)typ | objtyp);
 	}
-
 	return ret;
 }
 
+// same as runtime·new, but callable from C
+void*
+runtime·cnew(Type *typ)
+{
+	return cnew(typ, 1, TypeInfo_SingleObject);
+}
+
+void*
+runtime·cnewarray(Type *typ, intgo n)
+{
+	return cnew(typ, n, TypeInfo_Array);
+}
+
 func GC() {
 	runtime·gc(1);
 }

src/pkg/runtime/malloc.h

@@ -458,6 +458,7 @@ bool	runtime·blockspecial(void*);
 void	runtime·setblockspecial(void*, bool);
 void	runtime·purgecachedstats(MCache*);
 void*	runtime·cnew(Type*);
+void*	runtime·cnewarray(Type*, intgo);
 
 void	runtime·settype(void*, uintptr);
 void	runtime·settype_flush(M*, bool);

src/pkg/runtime/slice.c

@@ -51,27 +51,9 @@ uintptr runtime·zerobase;
 static void
 makeslice1(SliceType *t, intgo len, intgo cap, Slice *ret)
 {
-	uintptr size;
-
-	size = cap*t->elem->size;
-
 	ret->len = len;
 	ret->cap = cap;
-
-	if(size == 0)
-		ret->array = (byte*)&runtime·zerobase;
-	else if((t->elem->kind&KindNoPointers))
-		ret->array = runtime·mallocgc(size, FlagNoPointers, 1, 1);
-	else {
-		ret->array = runtime·mallocgc(size, 0, 1, 1);
-
-		if(UseSpanType) {
-			if(false) {
-				runtime·printf("new slice [%D]%S: %p\n", (int64)cap, *t->elem->string, ret->array);
-			}
-			runtime·settype(ret->array, (uintptr)t->elem | TypeInfo_Array);
-		}
-	}
+	ret->array = runtime·cnewarray(t->elem, cap);
 }
 
 // appendslice(type *Type, x, y, []T) []T