Comments.

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

diff --git a/src/userprog/exception.c b/src/userprog/exception.c
index dead766fdbde82b736394f1fc4c8ab92d371ff37..745adaa086e4614245748ddd3cbc6c6262b1f5de 100644 (file)
--- a/src/userprog/exception.c
+++ b/src/userprog/exception.c
@@ -5,6 +5,9 @@
 #include "threads/interrupt.h"
 #include "threads/thread.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 *);
 
 static void kill (struct intr_frame *);
 static void page_fault (struct intr_frame *);
 


@@ -54,6 +57,13 @@ exception_init (void)
   intr_register (14, 0, INTR_OFF, page_fault, "#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. */
 static void
 kill (struct intr_frame *f) 
 /* Handler for an exception (probably) caused by a user process. */
 static void
 kill (struct intr_frame *f) 


@@ -101,7 +111,8 @@ kill (struct intr_frame *f)
 #define PF_U 0x4    /* 0: kernel, 1: user process. */
 
 /* Page fault handler.  This is a skeleton that must be filled in
 #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.
+   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
 
    At entry, the address that faulted is in CR2 (Control Register
    2) and information about the fault, formatted as described in


@@ -113,21 +124,27 @@ kill (struct intr_frame *f)
 static void
 page_fault (struct intr_frame *f) 
 {
 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. */
+  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));
   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 ();
 
   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;
   /* Determine cause. */
   not_present = (f->error_code & PF_P) == 0;
   write = (f->error_code & PF_W) != 0;


@@ -136,7 +153,7 @@ page_fault (struct intr_frame *f)
   /* 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. */
   /* 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",
+  printf ("Page fault at %p: %s error %s page in %s context.\n",

           fault_addr,
           not_present ? "not present" : "rights violation",
           write ? "writing" : "reading",
           fault_addr,
           not_present ? "not present" : "rights violation",
           write ? "writing" : "reading",