+/* Page fault error code bits that describe the cause of the exception. */
+#define PF_P 0x1 /* 0: not-present page. 1: access rights violation. */
+#define PF_W 0x2 /* 0: read, 1: write. */
+#define PF_U 0x4 /* 0: kernel, 1: user process. */
+
+/* Page fault handler. This is a skeleton that must be filled in
+ to implement virtual memory. Some solutions to project 2 may
+ also require modifying this code.
+
+ At entry, the address that faulted is in CR2 (Control Register
+ 2) and information about the fault, formatted as described in
+ the PF_* macros above, is in F's error_code member. The
+ example code here shows how to parse that information. You
+ can find more information about both of these in the
+ description of "Interrupt 14--Page Fault Exception (#PF)" in
+ [IA32-v3] section 5.14, which is pages 5-46 to 5-49. */
+static void
+page_fault (struct intr_frame *f)
+{
+ bool not_present, write, user;
+ uint32_t fault_addr;
+
+ /* Obtain faulting address, then turn interrupts back on.
+ (Interrupts were only off so that we could be assured of
+ reading CR2 before it changed.)
+
+ The faulting address is not necesarily the address of the
+ instruction that caused the fault--that's in F's eip
+ member. Rather, it's the linear address that was accessed
+ to cause the fault, which is probably an address of data,
+ not code. */
+ asm ("movl %%cr2, %0" : "=r" (fault_addr));
+ intr_enable ();
+
+ /* Determine cause. */
+ not_present = (f->error_code & PF_P) == 0;
+ write = (f->error_code & PF_W) != 0;
+ user = (f->error_code & PF_U) != 0;
+
+ /* To implement virtual memory, delete the rest of the function
+ body, and replace it with code that brings in the page to
+ which fault_addr refers. */
+ printf ("Page fault at %08"PRIx32": %s error %s page in %s context.\n",
+ fault_addr,
+ not_present ? "not present" : "rights violation",
+ write ? "writing" : "reading",
+ user ? "user" : "kernel");
+ kill (f);
+}
+