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