From a0c44a30cf6731df08fcede2f54f069397ee36e9 Mon Sep 17 00:00:00 2001
From: Matthew Parkinson <mattpark@microsoft.com>
Date: Sun, 18 Dec 2022 22:47:41 +0000
Subject: [PATCH] Make reinterpret_cast more descriptive.

Add an operation to get a tag free pointer from an address_t, and use it
---
 src/snmalloc/aal/address.h  | 9 +++++++++
 src/snmalloc/mem/freelist.h | 2 +-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/snmalloc/aal/address.h b/src/snmalloc/aal/address.h
index 2a9d614ae..26824a4ee 100644
--- a/src/snmalloc/aal/address.h
+++ b/src/snmalloc/aal/address.h
@@ -290,4 +290,13 @@ namespace snmalloc
     return static_cast<size_t>(a - pointer_align_down<alignment>(a));
   }
 
+  /**
+   * Convert an address_t to a pointer.  The returned pointer should never be followed.
+   * On CHERI following this pointer will result in a capability violation.
+   */
+  template<typename T>
+  SNMALLOC_FAST_PATH_INLINE T* useless_ptr_from_addr(address_t p)
+  {
+    return reinterpret_cast<T*>(p);
+  }
 } // namespace snmalloc
diff --git a/src/snmalloc/mem/freelist.h b/src/snmalloc/mem/freelist.h
index ba7346f63..a4ad423a1 100644
--- a/src/snmalloc/mem/freelist.h
+++ b/src/snmalloc/mem/freelist.h
@@ -695,7 +695,7 @@ namespace snmalloc
           // the Freelist builder always knows which block it is referring too.
           head[i] = Object::code_next(
             address_cast(&head[i]),
-            reinterpret_cast<Object::T<BQueue>*>(slab),
+            useless_ptr_from_addr<Object::T<BQueue>>(address_cast(slab)),
             key);
         }
       }