ensure that integers cast to pointers will never point at a valid alloc, not even the zst alloc

src/error.rs

@@ -61,7 +61,7 @@ impl<'tcx> Error for EvalError<'tcx> {
             EvalError::DanglingPointerDeref =>
                 "dangling pointer was dereferenced",
             EvalError::InvalidFunctionPointer =>
-                "tried to use a pointer as a function pointer",
+                "tried to use an integer pointer as a function pointer",
             EvalError::InvalidBool =>
                 "invalid boolean value read",
             EvalError::InvalidDiscriminant =>

src/interpreter/terminator/mod.rs

@@ -639,7 +639,7 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
                 };
                 let drop_fn = self.memory.read_ptr(vtable)?;
                 // some values don't need to call a drop impl, so the value is null
-                if !drop_fn.points_to_zst() {
+                if drop_fn != Pointer::from_int(0) {
                     let (def_id, substs, ty) = self.memory.get_fn(drop_fn.alloc_id)?;
                     let fn_sig = self.tcx.erase_late_bound_regions_and_normalize(&ty.sig);
                     let real_ty = fn_sig.inputs[0];

src/memory.rs

@@ -73,7 +73,7 @@ impl Pointer {
     // FIXME(solson): Integer pointers should use u64, not usize. Target pointers can be larger
     // than host usize.
     pub fn from_int(i: usize) -> Self {
-        Pointer::new(ZST_ALLOC_ID, i)
+        Pointer::new(NEVER_ALLOC_ID, i)
     }
 
     pub fn zst_ptr() -> Self {
@@ -290,7 +290,7 @@ impl<'a, 'tcx> Memory<'a, 'tcx> {
             Some(alloc) => Ok(alloc),
             None => match self.functions.get(&id) {
                 Some(_) => Err(EvalError::DerefFunctionPointer),
-                None if id == ZST_ALLOC_ID => Err(EvalError::InvalidMemoryAccess),
+                None if id == NEVER_ALLOC_ID || id == ZST_ALLOC_ID => Err(EvalError::InvalidMemoryAccess),
                 None => Err(EvalError::DanglingPointerDeref),
             }
         }
@@ -302,7 +302,7 @@ impl<'a, 'tcx> Memory<'a, 'tcx> {
             Some(alloc) => Ok(alloc),
             None => match self.functions.get(&id) {
                 Some(_) => Err(EvalError::DerefFunctionPointer),
-                None if id == ZST_ALLOC_ID => Err(EvalError::InvalidMemoryAccess),
+                None if id == NEVER_ALLOC_ID || id == ZST_ALLOC_ID => Err(EvalError::InvalidMemoryAccess),
                 None => Err(EvalError::DanglingPointerDeref),
             }
         }

tests/run-pass/assume_bug.rs

@@ -0,0 +1,3 @@
+fn main() {
+    vec![()].into_iter();
+}