Prepare for PAL address_bits

src/pal/pal_concept.h

@@ -26,11 +26,12 @@ namespace snmalloc
   };
 
   /**
-   * PALs must advertise their page size
+   * PALs must advertise the size of the address space and their page size
    */
   template<typename PAL>
   concept ConceptPAL_static_sizes = requires()
   {
+    typename std::integral_constant<std::size_t, PAL::address_bits>;
     typename std::integral_constant<std::size_t, PAL::page_size>;
   };
 

src/pal/pal_noalloc.h

@@ -37,6 +37,8 @@ namespace snmalloc
 
     static constexpr size_t page_size = BasePAL::page_size;
 
+    static constexpr size_t address_bits = Aal::address_bits;
+
     /**
      * Print a stack trace.
      */

src/pal/pal_posix.h

@@ -132,6 +132,18 @@ namespace snmalloc
 
     static constexpr size_t page_size = Aal::smallest_page_size;
 
+    /**
+     * Address bits are potentially mediated by some POSIX OSes, but generally
+     * default to the architecture's.
+     *
+     * Unlike the AALs, which are composited by explicitly delegating to their
+     * template parameters and so play a SFINAE-based game to achieve similar
+     * ends, for the PALPOSIX<> classes we instead use more traditional
+     * inheritance (e.g., PALLinux is subtype of PALPOSIX<PALLinux>) and so we
+     * can just use that mechanism here, too.
+     */
+    static constexpr size_t address_bits = Aal::address_bits;
+
     static void print_stack_trace()
     {
 #ifdef SNMALLOC_BACKTRACE_HEADER

src/pal/pal_windows.h

@@ -62,6 +62,11 @@ namespace snmalloc
 
     static constexpr size_t page_size = 0x1000;
 
+    /**
+     * Windows always inherits its underlying architecture's full address range.
+     */
+    static constexpr size_t address_bits = Aal::address_bits;
+
     /**
      * Check whether the low memory state is still in effect.  This is an
      * expensive operation and should not be on any fast paths.