/**
* The exception handler. This handler is called by the processor whenever
* a user instruction causes a processor exception.
*
* <p>
* When the exception handler is invoked, interrupts are enabled, and the
* processor's cause register contains an integer identifying the cause of
* the exception (see the <tt>exceptionZZZ</tt> constants in the
* <tt>Processor</tt> class). If the exception involves a bad virtual
* address (e.g. page fault, TLB miss, read-only, bus error, or address
* error), the processor's BadVAddr register identifies the virtual address
* that caused the exception.
*/
public void exceptionHandler() {
Lib.assert(KThread.currentThread() instanceof UThread);
UserProcess process = ((UThread) KThread.currentThread()).process;
int cause = Machine.processor().readRegister(Processor.regCause);
process.handleException(cause);
}
/**
* Start running user programs, by creating a process and running a shell
* program in it. The name of the shell program it must run is returned by
* <tt>Machine.getShellProgramName()</tt>.
*
* @see nachos.machine.Machine#getShellProgramName
*/
public void run() {
super.run();
UserProcess process = UserProcess.newUserProcess();
String shellProgram = Machine.getShellProgramName();
Lib.assert(process.execute(shellProgram, new String[] { }));
KThread.currentThread().finish();
}
/**
* Returns the current process.
*
* @return the current process, or <tt>null</tt> if no process is current.
*/
public static UserProcess currentProcess() {
if (!(KThread.currentThread() instanceof UThread))
return null;
return ((UThread) KThread.currentThread()).process;
}