interp: defer out-of-bounds loads to runtime instead of crashing

interp/interp_test.go

@@ -20,6 +20,7 @@ func TestInterp(t *testing.T) {
 		"revert",
 		"store",
 		"alloc",
+		"slicedata",
 	} {
 		name := name // make local to this closure
 		t.Run(name, func(t *testing.T) {

interp/memory.go

@@ -299,7 +299,8 @@ func (mv *memoryView) put(index uint32, obj object) {
 }
 
 // Load the value behind the given pointer. Returns nil if the pointer points to
-// an external global.
+// an external global or if the load is out of bounds of the object (in which
+// case the caller defers the load to runtime).
 func (mv *memoryView) load(p pointerValue, size uint32) value {
 	if checks && mv.hasExternalStore(p) {
 		panic("interp: load from object with external store")
@@ -312,8 +313,13 @@ func (mv *memoryView) load(p pointerValue, size uint32) value {
 	if p.offset() == 0 && size == obj.size {
 		return obj.buffer.clone()
 	}
-	if checks && p.offset()+size > obj.size {
-		panic("interp: load out of bounds")
+	if p.offset()+size > obj.size {
+		// The load is out of bounds of the object. This can happen for valid
+		// Go programs, for example when dereferencing the pointer returned by
+		// unsafe.SliceData on a zero-capacity slice (which points to a
+		// zero-sized object). Return nil so the caller defers this load to
+		// runtime instead of crashing the compiler.
+		return nil
 	}
 	v := obj.buffer.asRawValue(mv.r)
 	loadedBuf := v.buf[p.offset() : p.offset()+size]

interp/testdata/slicedata.ll

@@ -0,0 +1,23 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64--linux"
+
+; Reproduction of https://github.com/tinygo-org/tinygo/issues/4214.
+; Dereferencing the pointer returned by unsafe.SliceData on a zero-capacity
+; slice produces a load that is out of bounds of a zero-sized object. The
+; interp must defer this load to runtime instead of crashing the compiler.
+
+@main.zeroSized = global {} zeroinitializer
+@main.v = global i64 0
+
+define void @runtime.initAll() unnamed_addr {
+entry:
+  call void @main.init(ptr undef)
+  ret void
+}
+
+define internal void @main.init(ptr %context) unnamed_addr {
+entry:
+  %val = load i64, ptr @main.zeroSized
+  store i64 %val, ptr @main.v
+  ret void
+}

interp/testdata/slicedata.out.ll

@@ -0,0 +1,12 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64--linux"
+
+@main.zeroSized = local_unnamed_addr global {} zeroinitializer
+@main.v = local_unnamed_addr global i64 0
+
+define void @runtime.initAll() unnamed_addr {
+entry:
+  %val = load i64, ptr @main.zeroSized, align 8
+  store i64 %val, ptr @main.v, align 8
+  ret void
+}