From 2a318264ea493c62b8ec2fe110654e3177b49939 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Thu, 30 Aug 2018 11:04:48 +0200
Subject: [PATCH] also allow comparing pointers with integers so big that they
 cannot be equal

---
 src/operator.rs | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/src/operator.rs b/src/operator.rs
index 550e7014afa..576c4a271f9 100644
--- a/src/operator.rs
+++ b/src/operator.rs
@@ -148,11 +148,30 @@ fn ptr_eq(
                     left == right
                 }
             }
-            // Comparing ptr and integer -- we only allow compating with NULL
-            (Scalar::Ptr(_), Scalar::Bits { bits: 0, .. }) |
-            (Scalar::Bits { bits: 0, .. }, Scalar::Ptr(_)) => false,
-            // Nothing else is supported
-            _ => return err!(InvalidPointerMath),
+            // Comparing ptr and integer -- we allow compating with NULL, and with addresses
+            // so close to the end of the `usize` range that they cannot overlap with an allocation
+            // of the given size.
+            (Scalar::Ptr(ptr), Scalar::Bits { bits, size }) |
+            (Scalar::Bits { bits, size }, Scalar::Ptr(ptr)) => {
+                assert_eq!(size as u64, self.pointer_size().bytes());
+                if bits == 0 {
+                    // Nothing equals 0
+                    false
+                } else {
+                    // Compute the highest address at which this allocation could live
+                    let alloc = self.memory.get(ptr.alloc_id)?;
+                    let max_base_addr =
+                        (1u128 << self.pointer_size().bits()) - alloc.bytes.len() as u128;
+                    let max_addr = max_base_addr + ptr.offset.bytes() as u128;
+                    if bits > max_addr {
+                        // The integer is too big, this cannot possibly be equal
+                        false
+                    } else {
+                        // TODO: We could also take alignment into account
+                        return err!(InvalidPointerMath);
+                    }
+                }
+            }
         })
     }