/**
* 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();
}
/**
* Handle a user exception. Called by <tt>UserKernel.exceptionHandler()</tt> . The <i>cause</i>
* argument identifies which exception occurred; see the <tt>Processor.exceptionZZZ</tt>
* constants.
*
* @param cause the user exception that occurred.
*/
public void handleException(int cause) {
Processor processor = Machine.processor();
switch (cause) {
case Processor.exceptionTLBMiss:
handleTLBMiss();
break;
default:
super.handleException(cause);
break;
}
}
/*
* if the input arguments are negative, return -1
* @return the child process Id
*/
private int handleExec(int file, int argc, int argv) {
if (file < 0 || argc < 0 || argv < 0) {
return -1;
}
String fileName = readVirtualMemoryString(file, 256);
if (fileName == null) {
return -1;
}
String args[] = new String[argc];
int byteReceived, argAddress;
byte temp[] = new byte[4];
for (int i = 0; i < argc; i++) {
byteReceived = readVirtualMemory(argv + i * 4, temp);
if (byteReceived != 4) {
return -1;
}
argAddress = Lib.bytesToInt(temp, 0);
args[i] = readVirtualMemoryString(argAddress, 256);
if (args[i] == null) {
return -1;
}
}
UserProcess child = UserProcess.newUserProcess();
childProcess newProcessData = new childProcess(child);
child.myChildProcess = newProcessData;
if (child.execute(fileName, args)) {
map.put(child.process_id, newProcessData);
return child.process_id;
}
return -1;
}