exception.cc

linux的例子,就是下载后到自己的机子上去运行

// 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 <string.h>
#include "copyright.h"
#include "system.h"
#include "syscall.h"
#include "processmanager.h"
//#include "addrspace.h"
extern int fileoffset;
extern AddrSpace *space;
ProcessManager *pm=new ProcessManager();
extern Lock *lock[100];
int returnpid[100];
int time,id=0;
//----------------------------------------------------------------------
// 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 newExec(int which){
	space->InitRegisters();
	space->RestoreState();
	machine->Run();
	returnpid[which] = 1;
	ASSERT(false);
}

void AdjustPCRegs()
{
	int pc;
	pc = machine->ReadRegister(PCReg);
	machine->WriteRegister(PrevPCReg,pc);
	pc = machine->ReadRegister(NextPCReg);
	machine->WriteRegister(PCReg,pc);
	pc+=4;
	machine->WriteRegister(NextPCReg,pc);
}

SpaceId Exec(char* name)
{
	time++;
	printf("Exec run %d times\n",time); 
	int pid,ppid;
	OpenFile * executable = fileSystem->Open(name);
	Thread *th =new Thread(name);
	if(executable == NULL) {
		printf("Unable to open file %s\n",name);
		return -1;
	}
	th->space=space;
	th->space->AssignMem(executable);
	delete executable;
	ppid = id;
	printf("father Process ID is %d\n",ppid);
	pid=pm->Getpid(ppid);
	printf("The Process ID is %d\n",pid);
	id = pid;
	th->Fork(newExec,pid);
	while(returnpid[pid] == 0)
		currentThread->Yield();
	pm->Release(pid,0);
	id = ppid;
	AdjustPCRegs();
	return pid;
}
	

void
ExceptionHandler(ExceptionType which)
{
    char filename[128];
    int type = machine->ReadRegister(2);
    if (which == SyscallException){
	switch(type){
	case SC_Halt:
		DEBUG('a', "Shutdown, initiated by user program.\n");
   		interrupt->Halt();
		break;
    	case SC_Exec:
		strcpy(filename,machine->mainMemory+fileoffset);
		if(Exec(filename)==-1){
			printf("error!\n");
			interrupt->Halt();
			return;
		}
		break;
	case SC_Join:
		break;
	case SC_Exit:
		currentThread->Finish();
		break;
	default:
		printf("Unexpected SyscallException %d %d\n",which,type);
		ASSERT(FALSE);
    	}
    }
    else {
	printf("Unexpected user mode exception %d %d\n", which, type);
	ASSERT(FALSE);
    }
}