[clang][bytecode] Check for unknown size array pointers in InitField*

This can happen when the base pointer is an unknown size array, where
!isOnePastEnd(), but isPastEnd().

Fixes #153990

Author: tbaederr

clang/lib/AST/ByteCode/Interp.h

@@ -1640,6 +1640,9 @@ bool InitField(InterpState &S, CodePtr OpPC, uint32_t I) {
   const Pointer &Ptr = S.Stk.peek<Pointer>();
   if (!CheckRange(S, OpPC, Ptr, CSK_Field))
     return false;
+  if (!CheckArray(S, OpPC, Ptr))
+    return false;
+
   const Pointer &Field = Ptr.atField(I);
   Field.deref<T>() = Value;
   Field.initialize();
@@ -1652,6 +1655,9 @@ bool InitFieldActivate(InterpState &S, CodePtr OpPC, uint32_t I) {
   const Pointer &Ptr = S.Stk.peek<Pointer>();
   if (!CheckRange(S, OpPC, Ptr, CSK_Field))
     return false;
+  if (!CheckArray(S, OpPC, Ptr))
+    return false;
+
   const Pointer &Field = Ptr.atField(I);
   Field.deref<T>() = Value;
   Field.activate();
@@ -1663,7 +1669,13 @@ template <PrimType Name, class T = typename PrimConv<Name>::T>
 bool InitBitField(InterpState &S, CodePtr OpPC, const Record::Field *F) {
   assert(F->isBitField());
   const T &Value = S.Stk.pop<T>();
-  const Pointer &Field = S.Stk.peek<Pointer>().atField(F->Offset);
+  const Pointer &Ptr = S.Stk.peek<Pointer>();
+  if (!CheckRange(S, OpPC, Ptr, CSK_Field))
+    return false;
+  if (!CheckArray(S, OpPC, Ptr))
+    return false;
+
+  const Pointer &Field = Ptr.atField(F->Offset);
 
   if constexpr (needsAlloc<T>()) {
     T Result = S.allocAP<T>(Value.bitWidth());
@@ -1689,7 +1701,13 @@ bool InitBitFieldActivate(InterpState &S, CodePtr OpPC,
                           const Record::Field *F) {
   assert(F->isBitField());
   const T &Value = S.Stk.pop<T>();
-  const Pointer &Field = S.Stk.peek<Pointer>().atField(F->Offset);
+  const Pointer &Ptr = S.Stk.peek<Pointer>();
+  if (!CheckRange(S, OpPC, Ptr, CSK_Field))
+    return false;
+  if (!CheckArray(S, OpPC, Ptr))
+    return false;
+
+  const Pointer &Field = Ptr.atField(F->Offset);
 
   if constexpr (needsAlloc<T>()) {
     T Result = S.allocAP<T>(Value.bitWidth());

clang/test/AST/ByteCode/arrays.cpp

@@ -800,3 +800,23 @@ namespace ZeroSizeArrayRead {
   static_assert(s[0] == '0', ""); // both-error {{not an integral constant expression}} \
                                   // both-note {{read of dereferenced one-past-the-end pointer}}
 }
+
+namespace FAM {
+  char *strchr(const char *, int);
+
+  struct A {
+    char n, a[2];
+  };
+  struct B {
+    int n;
+    struct A a[]; // both-note {{here}}
+  };
+
+  const struct B b = {0, {{1, {2, 3}}, {4, {5, 6}}}};
+  void foo(void) { int sch = 0 != strchr(b.a[1].a, '\0'); }
+
+  int foo2() {
+    struct B b = {0, {{1, {2, 3}}, {4, {5, 6}}}}; // both-error {{initialization of flexible array member is not allowed}}
+    return 1;
+  }
+}