From eb2d8890de7e8382ef23568dbe43e897c9fda7fe Mon Sep 17 00:00:00 2001
From: Nathaniel Filardo <nwf20@cl.cam.ac.uk>
Date: Thu, 2 May 2019 19:01:22 +0100
Subject: [PATCH] Additional provenance preservation

---
 src/mem/alloc.h | 28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/src/mem/alloc.h b/src/mem/alloc.h
index 84c5460..c5732ce 100644
--- a/src/mem/alloc.h
+++ b/src/mem/alloc.h
@@ -363,7 +363,7 @@ namespace snmalloc
         Metaslab& meta = super->get_meta(slab);
 
         sizeclass_t sc = meta.sizeclass;
-        size_t slab_end = static_cast<size_t>(address_cast(slab) + SLAB_SIZE);
+        void* slab_end = pointer_offset(slab, SLAB_SIZE);
 
         return external_pointer<location>(p, sc, slab_end);
       }
@@ -372,8 +372,7 @@ namespace snmalloc
         Mediumslab* slab = Mediumslab::get(p);
 
         sizeclass_t sc = slab->get_sizeclass();
-        size_t slab_end =
-          static_cast<size_t>(address_cast(slab) + SUPERSLAB_SIZE);
+        void* slab_end = pointer_offset(slab, SUPERSLAB_SIZE);
 
         return external_pointer<location>(p, sc, slab_end);
       }
@@ -755,16 +754,23 @@ namespace snmalloc
 
     template<Boundary location>
     static uintptr_t
-    external_pointer(void* p, sizeclass_t sizeclass, size_t end_point)
+    external_pointer(void* p, sizeclass_t sizeclass, void* end_point)
     {
       size_t rsize = sizeclass_to_size(sizeclass);
-      size_t end_point_correction = location == End ?
-        (end_point - 1) :
-        (location == OnePastEnd ? end_point : (end_point - rsize));
-      size_t offset_from_end =
-        (end_point - 1) - static_cast<size_t>(address_cast(p));
-      size_t end_to_end = round_by_sizeclass(rsize, offset_from_end);
-      return end_point_correction - end_to_end;
+
+      void* end_point_correction = location == End ?
+        (static_cast<uint8_t*>(end_point) - 1) :
+        (location == OnePastEnd ? end_point :
+                                  (static_cast<uint8_t*>(end_point) - rsize));
+
+      ptrdiff_t offset_from_end =
+        (static_cast<uint8_t*>(end_point) - 1) - static_cast<uint8_t*>(p);
+
+      size_t end_to_end =
+        round_by_sizeclass(rsize, static_cast<size_t>(offset_from_end));
+
+      return address_cast<uint8_t>(
+        static_cast<uint8_t*>(end_point_correction) - end_to_end);
     }
 
     void init_message_queue()