From 0b37be71c29cc35173c60a643cf44af11ef2f769 Mon Sep 17 00:00:00 2001
From: Scott Olson <scott@solson.me>
Date: Thu, 17 Mar 2016 07:24:10 -0600
Subject: [PATCH] Change invalid pointer read panic into Err.

---
 src/error.rs  | 3 +++
 src/memory.rs | 8 ++++----
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/error.rs b/src/error.rs
index a05250e3b548..9d8830f0d534 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -7,6 +7,7 @@ pub enum EvalError {
     InvalidBool,
     PointerOutOfBounds,
     InvalidPointerAccess,
+    ReadBytesAsPointer,
 }
 
 pub type EvalResult<T> = Result<T, EvalError>;
@@ -19,6 +20,8 @@ impl Error for EvalError {
             EvalError::PointerOutOfBounds => "pointer offset outside bounds of allocation",
             EvalError::InvalidPointerAccess =>
                 "a raw memory access tried to access part of a pointer value as bytes",
+            EvalError::ReadBytesAsPointer =>
+                "attempted to read some raw bytes as a pointer address",
         }
     }
 
diff --git a/src/memory.rs b/src/memory.rs
index ae927865b4dd..d9d1a60111f4 100644
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -149,10 +149,10 @@ impl Memory {
         let bytes = &alloc.bytes[ptr.offset..ptr.offset + POINTER_SIZE];
         let offset = byteorder::NativeEndian::read_u64(bytes) as usize;
 
-        // TODO(tsion): Return an EvalError here instead of panicking.
-        let alloc_id = *alloc.relocations.get(&ptr.offset).unwrap();
-
-        Ok(Pointer { alloc_id: alloc_id, offset: offset })
+        match alloc.relocations.get(&ptr.offset) {
+            Some(&alloc_id) => Ok(Pointer { alloc_id: alloc_id, offset: offset }),
+            None => Err(EvalError::ReadBytesAsPointer),
+        }
     }
 
     // TODO(tsion): Detect invalid writes here and elsewhere.