Initial version

2021-10-11 22:27:00 +02:00 · 2021-10-11 22:27:00 +02:00 · 6f405265a5
commit 6f405265a5
102 changed files with 14486 additions and 0 deletions
--- a/code/userprog/exception.cc
+++ b/code/userprog/exception.cc
@ -0,0 +1,137 @@
+// exception.cc 
+//      Entry point into the Nachos kernel from user programs.
+//      There are two kinds of things that can cause control to
+//      transfer back to here from user code:
+//
+//      syscall -- The user code explicitly requests to call a procedure
+//      in the Nachos kernel.  Right now, the only function we support is
+//      "Halt".
+//
+//      exceptions -- The user code does something that the CPU can't handle.
+//      For instance, accessing memory that doesn't exist, arithmetic errors,
+//      etc.  
+//
+//      Interrupts (which can also cause control to transfer from user
+//      code into the Nachos kernel) are handled elsewhere.
+//
+// For now, this only handles the Halt() system call.
+// Everything else core dumps.
+//
+// Copyright (c) 1992-1993 The Regents of the University of California.
+// All rights reserved.  See copyright.h for copyright notice and limitation 
+// of liability and disclaimer of warranty provisions.
+
+#include "copyright.h"
+#include "system.h"
+#include "syscall.h"
+
+//----------------------------------------------------------------------
+// UpdatePC : Increments the Program Counter register in order to resume
+// the user program immediately after the "syscall" instruction.
+//----------------------------------------------------------------------
+static void
+UpdatePC ()
+{
+    int pc = machine->ReadRegister (PCReg);
+    machine->WriteRegister (PrevPCReg, pc);
+    pc = machine->ReadRegister (NextPCReg);
+    machine->WriteRegister (PCReg, pc);
+    pc += 4;
+    machine->WriteRegister (NextPCReg, pc);
+}
+
+
+//----------------------------------------------------------------------
+// ExceptionHandler
+//      Entry point into the Nachos kernel.  Called when a user program
+//      is executing, and either does a syscall, or generates an addressing
+//      or arithmetic exception.
+//
+//      For system calls, the following is the calling convention:
+//
+//      system call code -- r2
+//              arg1 -- r4
+//              arg2 -- r5
+//              arg3 -- r6
+//              arg4 -- r7
+//
+//      The result of the system call, if any, must be put back into r2. 
+//
+// And don't forget to increment the pc before returning. (Or else you'll
+// loop making the same system call forever!
+//
+//      "which" is the kind of exception.  The list of possible exceptions 
+//      are in machine.h.
+//----------------------------------------------------------------------
+
+void
+ExceptionHandler (ExceptionType which)
+{
+    int type = machine->ReadRegister (2);
+    int address = machine->registers[BadVAddrReg];
+
+    switch (which)
+      {
+	case SyscallException:
+          {
+	    switch (type)
+	      {
+		case SC_Halt:
+		  {
+		    DEBUG ('s', "Shutdown, initiated by user program.\n");
+		    interrupt->Powerdown ();
+		    break;
+		  }
+		default:
+		  {
+		    printf("Unimplemented system call %d\n", type);
+		    ASSERT(FALSE);
+		  }
+	      }
+
+	    // Do not forget to increment the pc before returning!
+	    UpdatePC ();
+	    break;
+	  }
+
+	case PageFaultException:
+	  if (!address) {
+	    printf("NULL dereference at PC %x!\n", machine->registers[PCReg]);
+	    ASSERT (FALSE);
+	  } else {
+	    printf ("Page Fault at address %x at PC %x\n", address, machine->registers[PCReg]);
+	    ASSERT (FALSE);	// For now
+	  }
+	  break;
+
+	case ReadOnlyException:
+	  printf ("Read-Only at address %x at PC %x\n", address, machine->registers[PCReg]);
+	  ASSERT (FALSE);	// For now
+	  break;
+
+	case BusErrorException:
+	  printf ("Invalid physical address at address %x at PC %x\n", address, machine->registers[PCReg]);
+	  ASSERT (FALSE);	// For now
+	  break;
+
+	case AddressErrorException:
+	  printf ("Invalid address %x at PC %x\n", address, machine->registers[PCReg]);
+	  ASSERT (FALSE);	// For now
+	  break;
+
+	case OverflowException:
+	  printf ("Overflow at PC %x\n", machine->registers[PCReg]);
+	  ASSERT (FALSE);	// For now
+	  break;
+
+	case IllegalInstrException:
+	  printf ("Illegal instruction at PC %x\n", machine->registers[PCReg]);
+	  ASSERT (FALSE);	// For now
+	  break;
+
+	default:
+	  printf ("Unexpected user mode exception %d %d %x at PC %x\n", which, type, address, machine->registers[PCReg]);
+	  ASSERT (FALSE);
+	  break;
+      }
+}