Add other useful page-size-related fields to System module

src/core/System.cc

@@ -2,17 +2,42 @@
 #include <stdio.h>
 #include <unistd.h>
 #include <sys/mman.h>
+#include <stdint.h>
 
-long System::page_size;
+unsigned long System::page_size;
+unsigned int System::page_size_log;
+unsigned long System::page_base_mask;
+unsigned long System::page_offset_mask;
 
 bool System::init()
 {
-    System::page_size = sysconf(_SC_PAGESIZE);
+    long sc_page_size = sysconf(_SC_PAGESIZE);
-    if ((System::page_size == 0) ||
+    if (sc_page_size < 0)
-            (System::page_size > (2 * 1024 * 1024)) ||
-            ((System::page_size & (System::page_size - 1)) != 0))
     {
-        printf("Unsupported page size detected: %ld\n", System::page_size);
+        fprintf(stderr, "Unable to determine operating system page size.\n");
+        return false;
+    }
+
+    System::page_size = (unsigned long)sc_page_size;
+    System::page_size_log = 0u;
+    System::page_offset_mask = System::page_size - 1u;
+    System::page_base_mask = ~System::page_offset_mask;
+
+    for (uint_fast8_t i = 0u; i < 32u; i++)
+    {
+        unsigned long v = 1u << i;
+        if (v == System::page_size)
+        {
+            System::page_size_log = i;
+            break;
+        }
+    }
+
+    if ((System::page_size < 256u) ||
+            (System::page_size > (4u * 1024u * 1024u)) ||
+            (System::page_size_log == 0u))
+    {
+        fprintf(stderr, "Unsupported page size detected: 0x%lx\n", System::page_size);
         return false;
     }
 

src/core/System.h

@@ -5,8 +5,12 @@ class System
 {
 public:
     static bool init();
-    static long page_size;
     static void * alloc_pages(int num);
+
+    static unsigned long page_size;
+    static unsigned int page_size_log;
+    static unsigned long page_base_mask;
+    static unsigned long page_offset_mask;
 };
 
 #endif