X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fuserprog%2Fexception.c;h=745adaa086e4614245748ddd3cbc6c6262b1f5de;hb=e6e58461d3040e76e501a9dc9d4b38c5c825dc9c;hp=eaa069124e87a30de6fd0bbfc505f8ec8a792d68;hpb=6c5c6fdfe80bad40c90c19b67f00226610d59a38;p=pintos-anon

diff --git a/src/userprog/exception.c b/src/userprog/exception.c
index eaa0691..745adaa 100644
--- a/src/userprog/exception.c
+++ b/src/userprog/exception.c
@@ -1,18 +1,24 @@
-#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"
+
+/* Number of page faults processed. */
+static long long page_fault_cnt;
 
 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 +54,14 @@ 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");
+}
+
+/* Prints exception statistics. */
+void
+exception_print_stats (void) 
+{
+  printf ("Exception: %lld page faults\n", page_fault_cnt);
 }
 
 /* Handler for an exception (probably) caused by a user process. */
@@ -69,10 +82,9 @@ 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",
-              thread_name (thread_current ()),
-              f->vec_no, intr_name (f->vec_no));
+         expected.  Kill the user process.  */
+      printf ("%s: dying due to interrupt %#04x (%s).\n",
+              thread_name (), f->vec_no, intr_name (f->vec_no));
       intr_dump_frame (f);
       thread_exit (); 
 
@@ -80,15 +92,72 @@ 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.  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;  /* True: not-present page, false: writing r/o page. */
+  bool write;        /* True: access was write, false: access was read. */
+  bool user;         /* True: access by user, false: access by kernel. */
+  void *fault_addr;  /* Fault address. */
+
+  /* Obtain faulting address, the virtual address that was
+     accessed to cause the fault.  It may point to code or to
+     data.  It is not necessarily the address of the instruction
+     that caused the fault (that's f->eip).
+     See [IA32-v2a] "MOV--Move to/from Control Registers" and
+     [IA32-v3] 5.14 "Interrupt 14--Page Fault Exception
+     (#PF)". */
+  asm ("movl %%cr2, %0" : "=r" (fault_addr));
+
+  /* Turn interrupts back on (they were only off so that we could
+     be assured of reading CR2 before it changed). */
+  intr_enable ();
+
+  /* Count page faults. */
+  page_fault_cnt++;
+
+  /* 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 %p: %s error %s page in %s context.\n",
+          fault_addr,
+          not_present ? "not present" : "rights violation",
+          write ? "writing" : "reading",
+          user ? "user" : "kernel");
+  kill (f);
+}
+