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

src/interpreter/mod.rs

@@ -203,10 +203,6 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
         PrimVal::from_uint_with_size(n, self.memory.pointer_size())
     }
 
-    fn isize_primval(&self, n: i64) -> PrimVal {
-        PrimVal::from_int_with_size(n, self.memory.pointer_size())
-    }
-
     fn str_to_value(&mut self, s: &str) -> EvalResult<'tcx, Value> {
         // FIXME: cache these allocs
         let ptr = self.memory.allocate(s.len(), 1)?;
@@ -523,7 +519,8 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
                                 self.write_value(value, dest, value_ty)?;
                             } else {
                                 assert_eq!(operands.len(), 0);
-                                let zero = self.isize_primval(0);
+                                let value_size = self.type_size(dest_ty).expect("pointer types are sized");
+                                let zero = PrimVal::from_int_with_size(0, value_size);
                                 self.write_primval(dest, zero)?;
                             }
                         } else {
@@ -541,13 +538,14 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
                                     let operand_ty = self.operand_ty(operand);
                                     assert_eq!(self.type_size(operand_ty), Some(0));
                                 }
-                                let offset = self.nonnull_offset(dest_ty, nndiscr, discrfield)?;
+                                let (offset, ty) = self.nonnull_offset_and_ty(dest_ty, nndiscr, discrfield)?;
 
                                 // FIXME(solson)
                                 let dest = self.force_allocation(dest)?.to_ptr();
 
                                 let dest = dest.offset(offset.bytes() as isize);
-                                try!(self.memory.write_isize(dest, 0));
+                                let dest_size = self.type_size(ty).unwrap_or(self.memory.pointer_size());
+                                try!(self.memory.write_int(dest, 0, dest_size));
                             }
                         } else {
                             bug!("tried to assign {:?} to Layout::RawNullablePointer", kind);
@@ -694,7 +692,7 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
         }
     }
 
-    fn nonnull_offset(&self, ty: Ty<'tcx>, nndiscr: u64, discrfield: &[u32]) -> EvalResult<'tcx, Size> {
+    fn nonnull_offset_and_ty(&self, ty: Ty<'tcx>, nndiscr: u64, discrfield: &[u32]) -> EvalResult<'tcx, (Size, Ty<'tcx>)> {
         // Skip the constant 0 at the start meant for LLVM GEP.
         let mut path = discrfield.iter().skip(1).map(|&i| i as usize);
 
@@ -709,10 +707,10 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
             _ => bug!("non-enum for StructWrappedNullablePointer: {}", ty),
         };
 
-        self.field_path_offset(inner_ty, path)
+        self.field_path_offset_and_ty(inner_ty, path)
     }
 
-    fn field_path_offset<I: Iterator<Item = usize>>(&self, mut ty: Ty<'tcx>, path: I) -> EvalResult<'tcx, Size> {
+    fn field_path_offset_and_ty<I: Iterator<Item = usize>>(&self, mut ty: Ty<'tcx>, path: I) -> EvalResult<'tcx, (Size, Ty<'tcx>)> {
         let mut offset = Size::from_bytes(0);
 
         // Skip the initial 0 intended for LLVM GEP.
@@ -722,7 +720,7 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
             offset = offset.checked_add(field_offset, &self.tcx.data_layout).unwrap();
         }
 
-        Ok(offset)
+        Ok((offset, ty))
     }
 
     fn get_field_ty(&self, ty: Ty<'tcx>, field_index: usize) -> EvalResult<'tcx, Ty<'tcx>> {

src/interpreter/terminator/mod.rs

@@ -263,14 +263,17 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
                 self.memory.read_int(adt_ptr, discr_size as usize)? as u64
             }
 
-            RawNullablePointer { nndiscr, .. } => {
-                self.read_nonnull_discriminant_value(adt_ptr, nndiscr)?
+            RawNullablePointer { nndiscr, value } => {
+                let discr_size = value.size(&self.tcx.data_layout).bytes() as usize;
+                self.read_nonnull_discriminant_value(adt_ptr, nndiscr, discr_size)?
             }
 
             StructWrappedNullablePointer { nndiscr, ref discrfield, .. } => {
-                let offset = self.nonnull_offset(adt_ty, nndiscr, discrfield)?;
+                let (offset, ty) = self.nonnull_offset_and_ty(adt_ty, nndiscr, discrfield)?;
                 let nonnull = adt_ptr.offset(offset.bytes() as isize);
-                self.read_nonnull_discriminant_value(nonnull, nndiscr)?
+                // only the pointer part of a fat pointer is used for this space optimization
+                let discr_size = self.type_size(ty).unwrap_or(self.memory.pointer_size());
+                self.read_nonnull_discriminant_value(nonnull, nndiscr, discr_size)?
             }
 
             // The discriminant_value intrinsic returns 0 for non-sum types.
@@ -281,8 +284,8 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
         Ok(discr_val)
     }
 
-    fn read_nonnull_discriminant_value(&self, ptr: Pointer, nndiscr: u64) -> EvalResult<'tcx, u64> {
-        let not_null = match self.memory.read_usize(ptr) {
+    fn read_nonnull_discriminant_value(&self, ptr: Pointer, nndiscr: u64, discr_size: usize) -> EvalResult<'tcx, u64> {
+        let not_null = match self.memory.read_uint(ptr, discr_size) {
             Ok(0) => false,
             Ok(_) | Err(EvalError::ReadPointerAsBytes) => true,
             Err(e) => return Err(e),

tests/run-pass/small_enum_size_bug.rs

@@ -0,0 +1,14 @@
+#![allow(dead_code)]
+
+enum E {
+    A = 1,
+    B = 2,
+    C = 3,
+}
+
+fn main() {
+    let enone = None::<E>;
+    if let Some(..) = enone {
+        panic!();
+    }
+}