Add paging
diff --git a/src/paging.c b/src/paging.c
new file mode 100644
index 0000000..128de4e
--- /dev/null
+++ b/src/paging.c
@@ -0,0 +1,142 @@
+#include "paging.h"
+#include "io.h"
+#include "kint.h"
+#include "log.h"
+#include "pic.h"
+
+extern uint end;
+static size_t alloc_base = (size_t)&end;
+
+/* frames bitset, 0 = free, 1 = used */
+static uint *frames;
+static ulong num_frames;
+
+static uint first_page_table[1024] __attribute__((aligned(4096)));
+static uint *page_directory[1024] __attribute__((aligned(4096)));
+
+static uint ***current_directory;
+
+void *_kmalloc(size_t size, bool align, void **phys)
+{
+ if (align && (alloc_base & 0xfff)) // if not yet aligned
+ {
+ alloc_base &= ~0xfff;
+ alloc_base += 0x1000;
+ }
+
+ if (phys)
+ {
+ *phys = (void *)alloc_base;
+ }
+
+ size_t addr = alloc_base;
+ alloc_base += size;
+ return (void *)addr;
+}
+
+void *kmalloc(size_t size)
+{
+ return _kmalloc(size, false, NULL);
+}
+
+void *kmalloc_a(size_t size)
+{
+ return _kmalloc(size, true, NULL);
+}
+
+void *kmalloc_ap(size_t size, void **p)
+{
+ return _kmalloc(size, true, p);
+}
+
+/* frame utils */
+
+#define BITS 32
+
+static void set_frame(size_t frame_addr)
+{
+ uint frame = frame_addr / 0x1000; // page aligned
+ frames[frame / BITS] |= 1 << (frame % BITS);
+}
+
+static bool test_frame(size_t frame_addr)
+{
+ uint frame = frame_addr / 0x1000; // page aligned
+ return frames[frame / BITS] & 1 << (frame % BITS);
+}
+
+static void clear_frame(size_t frame_addr)
+{
+ uint frame = frame_addr / 0x1000; // page aligned
+ frames[frame / BITS] &= ~(1 << (frame % BITS));
+}
+
+static uint first_free_frame()
+{
+ for (int i = 0; i < num_frames / BITS; i++)
+ {
+ /*
+ * If there are any zeroes, ~ will yield a non-zero result,
+ * meaning that there are pages free. Otherwise, check next set
+ */
+ if (!~frames[i])
+ continue;
+
+ for (int j = 0; j < BITS; j++)
+ {
+ if ((frames[i] & 1 << j) == 0)
+ {
+ /* found unused frame */
+ return i * BITS + j;
+ }
+ }
+ }
+
+ /* did not find a free frame, panic */
+ kpanic("first_free_frame failed! no free frames");
+}
+
+void alloc_frame(uint *page, bool for_kernel, bool writable)
+{
+ if (*page >> 12)
+ return; /* frame already allocated */
+
+ uint frame = first_free_frame();
+ // kprintf("first_free_frame found %d\n", frame);
+ set_frame(frame * 0x1000); /* mark as mapped */
+}
+
+void free_frame(uint page)
+{
+ clear_frame(page / 0x1000);
+}
+
+/* paging stuff */
+
+void initialize_paging()
+{
+ for (int i = 0; i < 1024; i++)
+ {
+ page_directory[i] = (uint *) 0b010; // kernel, rw, not present
+ }
+
+ for (int i = 0; i < 1024; i++)
+ {
+ first_page_table[i] = (i * 0x1000) | 3;
+ }
+
+ page_directory[0] = (uint *) (((size_t) (uint *) first_page_table) | 3);
+
+ kprintf("Set up page directory[0], %x\n", (uint)first_page_table);
+
+ load_page_directory((uint) page_directory);
+ enable_paging();
+
+ add_interrupt_handler(14, page_fault);
+}
+
+void page_fault(struct registers *regs)
+{
+ kprintf("Page fault! eip = %d\n", regs->eip);
+ kpanic("Page fault");
+}