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[pintos-anon] / src / userprog / exception.c

diff --git a/src/userprog/exception.c b/src/userprog/exception.c
index eaa069124e87a30de6fd0bbfc505f8ec8a792d68..4e9d28ffd321204709afaabc0ea22f023e53296f 100644 (file)
--- a/src/userprog/exception.c
+++ b/src/userprog/exception.c
@@ -1,18 +1,21 @@
-#include "exception.h"
-#include "lib.h"
-#include "gdt.h"
-#include "interrupt.h"
-#include "thread.h"
+#include "userprog/exception.h"
+#include <inttypes.h>
+#include <stdio.h>
+#include "userprog/gdt.h"
+#include "threads/interrupt.h"
+#include "threads/thread.h"
 
 static void kill (struct intr_frame *);
+static void page_fault (struct intr_frame *);
 
 /* Registers handlers for interrupts that can be caused by user
    programs.
 
    In a real Unix-like OS, most of these interrupts would be
-   passed along to the user process in the form of signals, but
-   we don't implement signals.  Instead, we'll make them simply
-   kill the user process.
+   passed along to the user process in the form of signals, as
+   described in [SV-386] 3-24 and 3-25, but we don't implement
+   signals.  Instead, we'll make them simply kill the user
+   process.
 
    Page faults are an exception.  Here they are treated the same
    way as other exceptions, but this will need to change to
@@ -48,7 +51,7 @@ exception_init (void)
   /* Most exceptions can be handled with interrupts turned on.
      We need to disable interrupts for page faults because the
      fault address is stored in CR2 and needs to be preserved. */
-  intr_register (14, 0, INTR_OFF, kill, "#PF Page-Fault Exception");
+  intr_register (14, 0, INTR_OFF, page_fault, "#PF Page-Fault Exception");
 }
 
 /* Handler for an exception (probably) caused by a user process. */
@@ -69,8 +72,8 @@ kill (struct intr_frame *f)
     {
     case SEL_UCSEG:
       /* User's code segment, so it's a user exception, as we
-         expected. */
-      printk ("%s: dying due to interrupt %#04x (%s).\n",
+         expected.  Kill the user process.  */
+      printf ("%s: dying due to interrupt %#04x (%s).\n",
               thread_name (thread_current ()),
               f->vec_no, intr_name (f->vec_no));
       intr_dump_frame (f);
@@ -80,15 +83,65 @@ kill (struct intr_frame *f)
       /* Kernel's code segment, which indicates a kernel bug.
          Kernel code shouldn't throw exceptions.  (Page faults
          may cause kernel exceptions--but they shouldn't arrive
-         here.) */
+         here.)  Panic the kernel to make the point.  */
       intr_dump_frame (f);
       PANIC ("Kernel bug - unexpected interrupt in kernel"); 
 
     default:
-      /* Some other code segment?  Shouldn't happen. */
-      printk ("Interrupt %#04x (%s) in unknown segment %04x\n",
+      /* Some other code segment?  Shouldn't happen.  Panic the
+         kernel. */
+      printf ("Interrupt %#04x (%s) in unknown segment %04x\n",
              f->vec_no, intr_name (f->vec_no), f->cs);
       thread_exit ();
     }
 }
 
+/* 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.
+
+   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);
+}
+