Add C functions to construct paging structures

src/mem.c

+/*
+  mem.c is the main file for dealing with virtual memory and paging.
+*/
+
+#include "mem.h"
+
+// page_directory is currently defined once and should not be touched
+// later. It must be page aligned for the MMU to read properly
+uint32_t page_directory[1024] __attribute__((aligned(4096)));
+
+// page_table_one is the first page table, and at the beginning the
+// only page table in the page directory
+uint32_t page_table_one[1024] __attribute__((aligned(4096)));
+
+uint32_t* initiate_directory() {
+    // set each entry to not present
+    int i;
+    for(i = 0; i < 1024; i++)
+    {
+        // This sets the following flags to the pages:
+        //   Supervisor: Only kernel-mode can access them
+        //   Write Enabled: It can be both read from and written to
+        //     (this is the 2 bit)
+        //   Not Present: The page table is not present
+        page_directory[i] = 0x00000002;
+    }
+
+    return page_directory;
+}
+
+void initiate_page_table(uint32_t* page_dir) {
+    // holds the physical address where we want to start mapping these pages to.
+    // in this case, we want to map these pages to the very beginning of memory.
+    unsigned int i;
+
+    //we will fill all 1024 entries in the table, mapping 4 megabytes
+    for(i = 0; i < 1024; i++)
+    {
+        // As the address is page aligned, it will always leave 12 bits zeroed.
+        // Those bits are used by the attributes:
+        //    -> supervisor level, read/write, present.
+        page_table_one[i] = (i * 0x1000) | 3;
+    }
+
+    // attributes: supervisor level, read/write, present
+    page_dir[0] = ((unsigned int)page_table_one) | 3;
+}

src/mem.h

+/*
+  mem.h
+*/
+
+#pragma once
+#include <stdint.h>
+
+// Defined in the file mem.c
+uint32_t* initiate_directory();
+ void initiate_page_table(uint32_t* page_dir);