Nucleus

diff --git a/memory/paging.c b/memory/paging.c
new file mode 100644
index 0000000..b4f505e
--- /dev/null
+++ b/memory/paging.c
@@ -0,0 +1,90 @@
+/*
+ * This file contains all the functions used to manipulate the virtual address
+ * spaces.  It controls all of the system's paging and virtual memory from a low
+ * level perspective.  On initialisation, a page directory is allocated for the
+ * kernel that identity maps everything.
+ */
+
+#include <stdint.h>
+#include <string.h>
+#include <nucleus/memory.h>
+#include "paging.h"
+
+/* Switch page directory */
+static void
+switch_dir(page_dir_t dir)
+{
+	asm volatile("mov %0, %%cr3" :: "r" (dir));
+}
+
+/* Set a page mapping */
+void
+set_page(uintptr_t vaddr, page_t page)
+{
+	page_t *mappings = (void *) 0xFFC00000;
+	page_table_t *tables = (void *) 0xFFFFF000;
+	uintptr_t address = vaddr >> 12;
+	uint32_t tbl = address / 1024;
+	/* Create table if not present */
+	if (!(tables[tbl] & PDE_PRESENT)) {
+		tables[tbl] = alloc_frame() | PDE_PRESENT | PDE_WRITE;
+		memset(mappings + (tbl * 1024), 0, PAGE_SIZE);
+	}
+	mappings[address] = page;
+}
+
+/* Initialise paging */
+void
+init_paging(void)
+{
+	uint16_t tbl, pg;
+	page_dir_t kernelDir = alloc_frame();
+	page_table_t *kernelTables = (page_table_t *) kernelDir;
+	page_t *table;
+	for (tbl = 0; tbl < 1024; tbl++)
+		kernelTables[tbl] = 0x00000000 | PDE_WRITE;
+	for (tbl = 0; tbl < 2; tbl++) {
+		table = (page_t *) alloc_frame();
+		kernelTables[tbl] = ((page_table_t) table)
+		                  | PDE_WRITE | PDE_PRESENT;
+		for (pg = 0; pg < 1024; pg++) {
+			/* Skip bottom page - catches NULL dereferences */
+			if (!tbl && !pg)
+				continue;
+			table[pg] = (((tbl * 1024) + pg) << 12)
+			          | PTE_WRITE | PTE_PRESENT | PTE_GLOBAL;
+		}
+	}
+	/* Map the directory into itself */
+	kernelTables[1023] = kernelDir | PDE_WRITE | PDE_PRESENT;
+
+	/*
+	 * By mapping the page directory as the last page table, the page
+	 * directory entries are read as page table entries, and the page
+	 * table entries become the pages. This means that each page contains
+	 * the contents of a page table, and the region in memory represented by
+	 * the last page table contains a contiguous list of all pages in
+	 * memory.  The very last page contains the contents of the page
+	 * directory itself.  This means that each virtual address space
+	 * contains it's own paging structures.
+	 */
+
+	/* Use kernel directory */
+	switch_dir(kernelDir);
+	register_exception(14, early_page_fault_handler);
+	asm volatile (
+		"movl %%cr0, %%eax;"
+		"orl $0x80000000, %%eax;"
+		"movl %%eax, %%cr0"
+		::: "eax"
+	);
+
+	/* Identity page the APIC registers */
+	set_page(lapicPtr, lapicPtr | PTE_PRESENT | PTE_WRITE | PTE_GLOBAL);
+	set_page(ioapicPtr, ioapicPtr | PTE_PRESENT | PTE_WRITE | PTE_GLOBAL);
+
+	/* Allocate a kernel stack */
+	uintptr_t stk;
+	for (stk = 0xF0400000; stk < 0xF0800000; stk += PAGE_SIZE)
+		set_page(stk, alloc_frame() | PTE_PRESENT | PTE_WRITE);
+}