address comments

src/memory.rs

@@ -39,7 +39,6 @@ pub struct Pointer {
 
 impl Pointer {
     pub fn offset(self, i: isize) -> Self {
-        // FIXME: prevent offsetting ZST ptrs in tracing mode
         Pointer { offset: (self.offset as isize + i) as usize, ..self }
     }
     pub fn points_to_zst(&self) -> bool {
@@ -47,7 +46,7 @@ impl Pointer {
     }
     fn zst_ptr() -> Self {
         Pointer {
-            alloc_id: AllocId(0),
+            alloc_id: ZST_ALLOC_ID,
             offset: 0,
         }
     }
@@ -76,6 +75,8 @@ pub struct Memory<'a, 'tcx> {
     pub layout: &'a TargetDataLayout,
 }
 
+const ZST_ALLOC_ID: AllocId = AllocId(0);
+
 impl<'a, 'tcx> Memory<'a, 'tcx> {
     pub fn new(layout: &'a TargetDataLayout) -> Self {
         let mut mem = Memory {
@@ -86,16 +87,16 @@ impl<'a, 'tcx> Memory<'a, 'tcx> {
             layout: layout,
         };
         // alloc id 0 is reserved for ZSTs, this is an optimization to prevent ZST
-        // (e.g. function pointers, (), [], ...) from requiring memory
+        // (e.g. function items, (), [], ...) from requiring memory
         let alloc = Allocation {
             bytes: Vec::new(),
             relocations: BTreeMap::new(),
             undef_mask: UndefMask::new(0),
         };
-        mem.alloc_map.insert(AllocId(0), alloc);
+        mem.alloc_map.insert(ZST_ALLOC_ID, alloc);
         // check that additional zst allocs work
         debug_assert!(mem.allocate(0).points_to_zst());
-        debug_assert!(mem.get(AllocId(0)).is_ok());
+        debug_assert!(mem.get(ZST_ALLOC_ID).is_ok());
         mem
     }
 
@@ -147,17 +148,13 @@ impl<'a, 'tcx> Memory<'a, 'tcx> {
     // TODO(solson): Track which allocations were returned from __rust_allocate and report an error
     // when reallocating/deallocating any others.
     pub fn reallocate(&mut self, ptr: Pointer, new_size: usize) -> EvalResult<'tcx, Pointer> {
-        if ptr.points_to_zst() {
-            if new_size != 0 {
-                return Ok(self.allocate(new_size));
-            } else {
-                return Ok(ptr);
-            }
-        }
         if ptr.offset != 0 {
             // TODO(solson): Report error about non-__rust_allocate'd pointer.
             return Err(EvalError::Unimplemented(format!("bad pointer offset: {}", ptr.offset)));
         }
+        if ptr.points_to_zst() {
+            return Ok(self.allocate(new_size));
+        }
 
         let size = self.get_mut(ptr.alloc_id)?.bytes.len();
 
@@ -187,10 +184,12 @@ impl<'a, 'tcx> Memory<'a, 'tcx> {
         }
 
         if self.alloc_map.remove(&ptr.alloc_id).is_none() {
+            debug!("deallocated a pointer twice: {}", ptr.alloc_id);
             // TODO(solson): Report error about erroneous free. This is blocked on properly tracking
             // already-dropped state since this if-statement is entered even in safe code without
             // it.
         }
+        debug!("deallocated : {}", ptr.alloc_id);
 
         Ok(())
     }

tests/compile-fail/out_of_bounds_read.rs

@@ -1,5 +1,5 @@
 fn main() {
     let v: Vec<u8> = vec![1, 2];
-    let x = unsafe { *v.get_unchecked(5) }; //~ ERROR: memory access of 5..6 outside bounds of allocation 31 which has size 2
+    let x = unsafe { *v.get_unchecked(5) }; //~ ERROR: which has size 2
     panic!("this should never print: {}", x);
 }

tests/compile-fail/out_of_bounds_read2.rs

@@ -0,0 +1,5 @@
+fn main() {
+    let v: Vec<u8> = vec![1, 2];
+    let x = unsafe { *v.get_unchecked(5) }; //~ ERROR: memory access of 5..6 outside bounds of allocation
+    panic!("this should never print: {}", x);
+}