Move user exception support into userprog.

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

diff --git a/src/userprog/exception.c b/src/userprog/exception.c
new file mode 100644 (file)
index 0000000..eaa0691
--- /dev/null
+++ b/src/userprog/exception.c
@@ -0,0 +1,94 @@
+#include "exception.h"
+#include "lib.h"
+#include "gdt.h"
+#include "interrupt.h"
+#include "thread.h"
+
+static void kill (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.
+
+   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-v3] section 5.14 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 (3, 3, INTR_ON, kill, "#BP Breakpoint Exception");
+  intr_register (4, 3, INTR_ON, kill, "#OF Overflow Exception");
+  intr_register (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 (0, 0, INTR_ON, kill, "#DE Divide Error");
+  intr_register (1, 0, INTR_ON, kill, "#DB Debug Exception");
+  intr_register (6, 0, INTR_ON, kill, "#UD Invalid Opcode Exception");
+  intr_register (7, 0, INTR_ON, kill, "#NM Device Not Available Exception");
+  intr_register (11, 0, INTR_ON, kill, "#NP Segment Not Present");
+  intr_register (12, 0, INTR_ON, kill, "#SS Stack Fault Exception");
+  intr_register (13, 0, INTR_ON, kill, "#GP General Protection Exception");
+  intr_register (16, 0, INTR_ON, kill, "#MF x87 FPU Floating-Point Error");
+  intr_register (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 (14, 0, INTR_OFF, kill, "#PF Page-Fault Exception");
+}
+
+/* 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. */
+      printk ("%s: dying due to interrupt %#04x (%s).\n",
+              thread_name (thread_current ()),
+              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.) */
+      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",
+             f->vec_no, intr_name (f->vec_no), f->cs);
+      thread_exit ();
+    }
+}
+