NFC: Split InvalidPointer out of ds/dllist.h

This lets us use Pagemaps without requiring dllists in scope

src/ds/dllist.h

@@ -1,59 +1,13 @@
 #pragma once
 
 #include "helpers.h"
+#include "invalidptr.h"
 
 #include <cstdint>
 #include <type_traits>
 
 namespace snmalloc
 {
-  /**
-   * Invalid pointer class.  This is similar to `std::nullptr_t`, but allows
-   * other values.
-   */
-  template<address_t Sentinel>
-  struct InvalidPointer
-  {
-    /**
-     * Equality comparison. Two invalid pointer values with the same sentinel
-     * are always the same, invalid pointer values with different sentinels are
-     * always different.
-     */
-    template<address_t OtherSentinel>
-    constexpr bool operator==(const InvalidPointer<OtherSentinel>&)
-    {
-      return Sentinel == OtherSentinel;
-    }
-    /**
-     * Equality comparison. Two invalid pointer values with the same sentinel
-     * are always the same, invalid pointer values with different sentinels are
-     * always different.
-     */
-    template<address_t OtherSentinel>
-    constexpr bool operator!=(const InvalidPointer<OtherSentinel>&)
-    {
-      return Sentinel != OtherSentinel;
-    }
-    /**
-     * Implicit conversion, creates a pointer with the value of the sentinel.
-     * On CHERI and other provenance-tracking systems, this is a
-     * provenance-free integer and so will trap if dereferenced, on other
-     * systems the sentinel should be a value in unmapped memory.
-     */
-    template<typename T>
-    operator T*() const
-    {
-      return reinterpret_cast<T*>(Sentinel);
-    }
-    /**
-     * Implicit conversion to an address, returns the sentinel value.
-     */
-    operator address_t() const
-    {
-      return Sentinel;
-    }
-  };
-
   template<
     class T,
     class Terminator = std::nullptr_t,

src/ds/invalidptr.h

@@ -0,0 +1,51 @@
+#pragma once
+
+namespace snmalloc
+{
+  /**
+   * Invalid pointer class.  This is similar to `std::nullptr_t`, but allows
+   * other values.
+   */
+  template<address_t Sentinel>
+  struct InvalidPointer
+  {
+    /**
+     * Equality comparison. Two invalid pointer values with the same sentinel
+     * are always the same, invalid pointer values with different sentinels are
+     * always different.
+     */
+    template<address_t OtherSentinel>
+    constexpr bool operator==(const InvalidPointer<OtherSentinel>&)
+    {
+      return Sentinel == OtherSentinel;
+    }
+    /**
+     * Equality comparison. Two invalid pointer values with the same sentinel
+     * are always the same, invalid pointer values with different sentinels are
+     * always different.
+     */
+    template<address_t OtherSentinel>
+    constexpr bool operator!=(const InvalidPointer<OtherSentinel>&)
+    {
+      return Sentinel != OtherSentinel;
+    }
+    /**
+     * Implicit conversion, creates a pointer with the value of the sentinel.
+     * On CHERI and other provenance-tracking systems, this is a
+     * provenance-free integer and so will trap if dereferenced, on other
+     * systems the sentinel should be a value in unmapped memory.
+     */
+    template<typename T>
+    operator T*() const
+    {
+      return reinterpret_cast<T*>(Sentinel);
+    }
+    /**
+     * Implicit conversion to an address, returns the sentinel value.
+     */
+    operator address_t() const
+    {
+      return Sentinel;
+    }
+  };
+} // namespace snmalloc

src/mem/pagemap.h

@@ -2,6 +2,7 @@
 
 #include "../ds/bits.h"
 #include "../ds/helpers.h"
+#include "../ds/invalidptr.h"
 
 #include <atomic>
 #include <utility>