runtime: require explicit GC layouts

interp/memory.go

@@ -1278,13 +1278,14 @@ func (r *runner) readObjectLayout(layoutValue value) (uint64, *big.Int) {
 	// integer value, or can be nil.
 	ptr, err := layoutValue.asPointer(r)
 	if err == errIntegerAsPointer {
-		// It's an integer, which means it's a small object or unknown.
+		// It's an integer, which means it's a small object.
 		layout := layoutValue.Uint(r)
 		if layout == 0 {
-			// Nil pointer, which means the layout is unknown.
-			return 0, nil
+			panic("runtime.alloc called without a GC layout")
 		}
 		if layout%2 != 1 {
+			// Conservative layouts are reserved for stack storage and cannot
+			// reach interpreted heap allocations.
 			// Sanity check: the least significant bit must be set. This is how
 			// the runtime can separate pointers from integers.
 			panic("unexpected layout")
@@ -1331,11 +1332,6 @@ func (r *runner) readObjectLayout(layoutValue value) (uint64, *big.Int) {
 // have some additional repetition, for example in the buffer of a slice.
 func (r *runner) getLLVMTypeFromLayout(layoutValue value) llvm.Type {
 	objectSizeWords, bitmap := r.readObjectLayout(layoutValue)
-	if bitmap == nil {
-		// No information available.
-		return llvm.Type{}
-	}
-
 	if bitmap.BitLen() == 0 {
 		// There are no pointers in this object, so treat this as a raw byte
 		// buffer. This is important because objects without pointers may have

interp/testdata/alloc.ll

@@ -11,6 +11,7 @@ target triple = "wasm32--wasi"
 @layout3 = global ptr null
 @layout4 = global ptr null
 @bigobj1 = global ptr null
+@pointerFree10 = global ptr null
 
 declare ptr @runtime.alloc(i32, ptr) unnamed_addr
 
@@ -49,5 +50,9 @@ define internal void @main.init() unnamed_addr {
   ; Large object that needs to be stored in a separate global.
   %bigobj1 = call ptr @runtime.alloc(i32 248, ptr @"runtime/gc.layout:62-2000000000000001")
   store ptr %bigobj1, ptr @bigobj1
+
+  ; Another pointer-free object.
+  %pointerFree10 = call ptr @runtime.alloc(i32 10, ptr inttoptr (i32 3 to ptr))
+  store ptr %pointerFree10, ptr @pointerFree10
   ret void
 }

interp/testdata/alloc.out.ll

@@ -10,6 +10,7 @@ target triple = "wasm32--wasi"
 @layout3 = local_unnamed_addr global ptr @"main$alloc.6"
 @layout4 = local_unnamed_addr global ptr @"main$alloc.7"
 @bigobj1 = local_unnamed_addr global ptr @"main$alloc.8"
+@pointerFree10 = local_unnamed_addr global ptr @"main$alloc.9"
 @"main$alloc" = internal global [12 x i8] zeroinitializer, align 4
 @"main$alloc.1" = internal global [7 x i8] zeroinitializer, align 4
 @"main$alloc.2" = internal global [3 x i8] zeroinitializer, align 4
@@ -19,6 +20,7 @@ target triple = "wasm32--wasi"
 @"main$alloc.6" = internal global { ptr, ptr, ptr, i32, i32, ptr, ptr, i32, i32, i32, i32, i32, i32, ptr, ptr, i32, i32, i32, ptr, ptr, i32, i32, ptr, i32, i32, ptr } zeroinitializer, align 4
 @"main$alloc.7" = internal global [3 x { ptr, ptr, ptr, i32, i32, ptr, ptr, i32, i32, i32, i32, i32, i32, ptr, ptr, i32, i32, i32, ptr, ptr, i32, i32, ptr, i32, i32, ptr }] zeroinitializer, align 4
 @"main$alloc.8" = internal global { ptr, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, ptr } zeroinitializer, align 4
+@"main$alloc.9" = internal global [10 x i8] zeroinitializer, align 4
 
 define void @runtime.initAll() unnamed_addr {
   ret void