1 files changed, 174 insertions, 0 deletions

diff --git a/userprog/exception.c b/userprog/exception.c
new file mode 100644
index 0000000..17620ad
--- /dev/null
+++ b/userprog/exception.c
@@ -0,0 +1,174 @@
+#include "userprog/exception.h"
+#include <inttypes.h>
+#include <stdio.h>
+#include "userprog/gdt.h"
+#include "threads/interrupt.h"
+#include "threads/thread.h"
+#include "threads/vaddr.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, 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
+   implement virtual memory.
+
+   Refer to [IA32-v3a] section 5.15 "Exception and Interrupt
+   Reference" for a description of each of these exceptions. */
+void
+exception_init (void) 
+{
+  /* These exceptions can be raised explicitly by a user program,
+     e.g. via the INT, INT3, INTO, and BOUND instructions.  Thus,
+     we set DPL==3, meaning that user programs are allowed to
+     invoke them via these instructions. */
+  intr_register_int (3, 3, INTR_ON, kill, "#BP Breakpoint Exception");
+  intr_register_int (4, 3, INTR_ON, kill, "#OF Overflow Exception");
+  intr_register_int (5, 3, INTR_ON, kill,
+                     "#BR BOUND Range Exceeded Exception");
+
+  /* These exceptions have DPL==0, preventing user processes from
+     invoking them via the INT instruction.  They can still be
+     caused indirectly, e.g. #DE can be caused by dividing by
+     0.  */
+  intr_register_int (0, 0, INTR_ON, kill, "#DE Divide Error");
+  intr_register_int (1, 0, INTR_ON, kill, "#DB Debug Exception");
+  intr_register_int (6, 0, INTR_ON, kill, "#UD Invalid Opcode Exception");
+  intr_register_int (7, 0, INTR_ON, kill,
+                     "#NM Device Not Available Exception");
+  intr_register_int (11, 0, INTR_ON, kill, "#NP Segment Not Present");
+  intr_register_int (12, 0, INTR_ON, kill, "#SS Stack Fault Exception");
+  intr_register_int (13, 0, INTR_ON, kill, "#GP General Protection Exception");
+  intr_register_int (16, 0, INTR_ON, kill, "#MF x87 FPU Floating-Point Error");
+  intr_register_int (19, 0, INTR_ON, kill,
+                     "#XF SIMD Floating-Point Exception");
+
+  /* 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_int (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) 
+{
+  /* This interrupt is one (probably) caused by a user process.
+     For example, the process might have tried to access unmapped
+     virtual memory (a page fault).  For now, we simply kill the
+     user process.  Later, we'll want to handle page faults in
+     the kernel.  Real Unix-like operating systems pass most
+     exceptions back to the process via signals, but we don't
+     implement them. */
+     
+  /* The interrupt frame's code segment value tells us where the
+     exception originated. */
+  switch (f->cs)
+    {
+    case SEL_UCSEG:
+      /* User's code segment, so it's a user exception, as we
+         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 (); 
+
+    case SEL_KCSEG:
+      /* 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.)  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.  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 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 in exception.h, 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-v3a] section 5.15 "Exception and Interrupt Reference". */
+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-v3a] 5.15 "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, adapt the rest of the function
+     body, adding code that brings in the page to
+     which fault_addr refers. */
+  if (is_user_vaddr(fault_addr)) {
+    if (! user) {
+      /* syscall exception; set eax and eip */
+      f->eip = (void*)f->eax;
+      f->eax = 0xFFFFFFFF;
+      return;
+    } else {
+      /* user process access violation */
+      thread_exit();
+    }
+  } else {
+    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);
+  }
+}
+