interp: keep partial loads independent of buffers owned by a caller's memory view

interp/memory.go

@@ -323,15 +323,25 @@ func (mv *memoryView) load(p pointerValue, size uint32) value {
 	}
 	v := obj.buffer.asRawValue(mv.r)
 	loadedBuf := v.buf[p.offset() : p.offset()+size]
-	if _, writable := mv.objects[p.index()]; writable {
-		// This object's buffer is owned by this view, which means a later
-		// store may mutate it in place (see store below). Copy the loaded
-		// slice so the returned value is not aliased with the live buffer.
-		loadedBuf = append([]uint64(nil), loadedBuf...)
+	if mv.owned(p.index()) {
+		// A store in an owning view may change the buffer in place, so copy
+		// the slice to keep the loaded value independent of it.
+		loadedBuf = slices.Clone(loadedBuf)
 	}
 	return rawValue{buf: loadedBuf}
 }
 
+// owned reports whether this view or a parent view holds the object, so that a
+// store in that view may change its buffer in place.
+func (mv *memoryView) owned(index uint32) bool {
+	for v := mv; v != nil; v = v.parent {
+		if _, ok := v.objects[index]; ok {
+			return true
+		}
+	}
+	return false
+}
+
 // Store to the value behind the given pointer. This overwrites the value in the
 // memory view, so that the changed value is discarded when the memory view is
 // reverted. Returns true on success, false if the object to store to is

interp/testdata/store.ll

@@ -6,13 +6,16 @@ target triple = "x86_64--linux"
 @alias.dst = global [2 x i8] zeroinitializer
 @reload.buf = global [4 x i8] c"\01\02\03\04"
 @reload.out = global [2 x i8] zeroinitializer
+@crosscall.buf = global [4 x i8] c"\01\02\03\04"
+@crosscall.out = global [2 x i8] zeroinitializer
 @struct.value = global { i8, i64, { i32, i8 } } zeroinitializer
 
 define void @runtime.initAll() unnamed_addr {
 entry:
   call void @overlap.init(ptr undef)
   call void @alias.init(ptr undef)
   call void @reload.init(ptr undef)
+  call void @crosscall.init(ptr undef)
   call void @struct.init(ptr undef)
   ret void
 }
@@ -50,6 +53,25 @@ entry:
   ret void
 }
 
+define internal void @crosscall.init(ptr %context) unnamed_addr {
+entry:
+  ; First store makes crosscall.buf writable in this memory view.
+  %tail = getelementptr [4 x i8], ptr @crosscall.buf, i32 0, i32 3
+  store i8 9, ptr %tail
+  ; Partial load in a callee, which has its own memory view.
+  %val = call i16 @crosscall.get(ptr undef)
+  ; In-place partial store in this view; this must not corrupt %val.
+  store i8 99, ptr @crosscall.buf
+  store i16 %val, ptr @crosscall.out
+  ret void
+}
+
+define internal i16 @crosscall.get(ptr %context) unnamed_addr {
+entry:
+  %val = load i16, ptr @crosscall.buf
+  ret i16 %val
+}
+
 define internal void @struct.init(ptr %context) unnamed_addr {
 entry:
   %b = getelementptr { i8, i64, { i32, i8 } }, ptr @struct.value, i32 0, i32 1

interp/testdata/store.out.ll

@@ -6,6 +6,8 @@ target triple = "x86_64--linux"
 @alias.dst = local_unnamed_addr global [2 x i8] c"\09\07"
 @reload.buf = local_unnamed_addr global [4 x i8] c"c\02\03\09"
 @reload.out = local_unnamed_addr global [2 x i8] c"\01\02"
+@crosscall.buf = local_unnamed_addr global [4 x i8] c"c\02\03\09"
+@crosscall.out = local_unnamed_addr global [2 x i8] c"\01\02"
 @struct.value = local_unnamed_addr global { i8, i64, { i32, i8 } } { i8 0, i64 42, { i32, i8 } { i32 0, i8 7 } }
 
 define void @runtime.initAll() unnamed_addr {

testdata/init.go

@@ -20,6 +20,7 @@ func main() {
 	println(uint8SliceDst[0])
 	println(intSliceSrc[0])
 	println(intSliceDst[0])
+	println("loaded:", loaded)
 }
 
 type (
@@ -112,6 +113,21 @@ func sliceSlice(s []int, start, end int) []int {
 
 type outside struct{}
 
+var (
+	loadPair struct{ a, b int }
+	loaded   int
+)
+
+func loadA() int { return loadPair.a }
+
+// The value loaded by loadA must not change when init stores to loadPair.a.
+func init() {
+	loadPair.a = 1
+	x := loadA()
+	loadPair.a = 2
+	loaded = x
+}
+
 func init() {
 	_, _ = any(0).(interface{ DoesNotExist() })
 	_, _ = any("").(interface{ DoesNotExist() })

testdata/init.txt

@@ -13,3 +13,4 @@ v9: 3 2 3 4
 3
 5
 5
+loaded: 1