// addrspace.cc //	Routines to manage address spaces (executing user programs).////	In order to run a user program, you must:////	1. link with the -N -T 0 option //	2. run coff2noff to convert the object file to Nachos format//		(Nachos object code format is essentially just a simpler//		version of the UNIX executable object code format)//	3. load the NOFF file into the Nachos file system//		(if you haven't implemented the file system yet, you//		don't need to do this last step)//// 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 "addrspace.h"#include "noff.h"#ifdef HOST_SPARC#include <strings.h>#endif//----------------------------------------------------------------------// SwapHeader// 	Do little endian to big endian conversion on the bytes in the //	object file header, in case the file was generated on a little//	endian machine, and we're now running on a big endian machine.//----------------------------------------------------------------------static void SwapHeader (NoffHeader *noffH){	noffH->noffMagic = WordToHost(noffH->noffMagic);	noffH->code.size = WordToHost(noffH->code.size);	noffH->code.virtualAddr = WordToHost(noffH->code.virtualAddr);	noffH->code.inFileAddr = WordToHost(noffH->code.inFileAddr);	noffH->initData.size = WordToHost(noffH->initData.size);	noffH->initData.virtualAddr = WordToHost(noffH->initData.virtualAddr);	noffH->initData.inFileAddr = WordToHost(noffH->initData.inFileAddr);	noffH->uninitData.size = WordToHost(noffH->uninitData.size);	noffH->uninitData.virtualAddr = WordToHost(noffH->uninitData.virtualAddr);	noffH->uninitData.inFileAddr = WordToHost(noffH->uninitData.inFileAddr);}//----------------------------------------------------------------------// AddrSpace::AddrSpace// 	Create an address space to run a user program.//	Load the program from a file "executable", and set everything//	up so that we can start executing user instructions.////	Assumes that the object code file is in NOFF format.////	First, set up the translation from program memory to physical //	memory.  For now, this is really simple (1:1), since we are//	only uniprogramming, and we have a single unsegmented page table////	"executable" is the file containing the object code to load into memory//----------------------------------------------------------------------AddrSpace::AddrSpace(OpenFile *executable){    NoffHeader noffH;    unsigned int i, size;    executable->ReadAt((char *)&noffH, sizeof(noffH), 0);    if ((noffH.noffMagic != NOFFMAGIC) && 		(WordToHost(noffH.noffMagic) == NOFFMAGIC))    	SwapHeader(&noffH);    ASSERT(noffH.noffMagic == NOFFMAGIC);// how big is address space?    size = noffH.code.size + noffH.initData.size + noffH.uninitData.size 			+ UserStackSize;	// we need to increase the size						// to leave room for the stack    numPages = divRoundUp(size, PageSize);    size = numPages * PageSize;    ASSERT(numPages <= NumPhysPages);		// check we're not trying						// to run anything too big --						// at least until we have						// virtual memory    DEBUG('a', "Initializing address space, num pages %d, size %d\n", 					numPages, size);// first, set up the translation     pageTable = new TranslationEntry[numPages];    for (i = 0; i < numPages; i++) {	pageTable[i].virtualPage = i;	// for now, virtual page # = phys page #	pageTable[i].physicalPage = i;	pageTable[i].valid = TRUE;	pageTable[i].use = FALSE;	pageTable[i].dirty = FALSE;	pageTable[i].readOnly = FALSE;  // if the code segment was entirely on 					// a separate page, we could set its 					// pages to be read-only    }    // zero out the entire address space, to zero the unitialized data segment // and the stack segment    bzero(machine->mainMemory, size);// then, copy in the code and data segments into memory    if (noffH.code.size > 0) {        DEBUG('a', "Initializing code segment, at 0x%x, size %d\n", 			noffH.code.virtualAddr, noffH.code.size);        executable->ReadAt(&(machine->mainMemory[noffH.code.virtualAddr]),			noffH.code.size, noffH.code.inFileAddr);    }    if (noffH.initData.size > 0) {        DEBUG('a', "Initializing data segment, at 0x%x, size %d\n", 			noffH.initData.virtualAddr, noffH.initData.size);        executable->ReadAt(&(machine->mainMemory[noffH.initData.virtualAddr]),			noffH.initData.size, noffH.initData.inFileAddr);    }}//----------------------------------------------------------------------// AddrSpace::~AddrSpace// 	Dealloate an address space.  Nothing for now!//----------------------------------------------------------------------AddrSpace::~AddrSpace(){   delete pageTable;}//----------------------------------------------------------------------// AddrSpace::InitRegisters// 	Set the initial values for the user-level register set.//// 	We write these directly into the "machine" registers, so//	that we can immediately jump to user code.  Note that these//	will be saved/restored into the currentThread->userRegisters//	when this thread is context switched out.//----------------------------------------------------------------------voidAddrSpace::InitRegisters(){    int i;    for (i = 0; i < NumTotalRegs; i++)	machine->WriteRegister(i, 0);    // Initial program counter -- must be location of "Start"    machine->WriteRegister(PCReg, 0);	    // Need to also tell MIPS where next instruction is, because    // of branch delay possibility    machine->WriteRegister(NextPCReg, 4);   // Set the stack register to the end of the address space, where we   // allocated the stack; but subtract off a bit, to make sure we don't   // accidentally reference off the end!    machine->WriteRegister(StackReg, numPages * PageSize - 16);    DEBUG('a', "Initializing stack register to %d\n", numPages * PageSize - 16);}//----------------------------------------------------------------------// AddrSpace::SaveState// 	On a context switch, save any machine state, specific//	to this address space, that needs saving.////	For now, nothing!//----------------------------------------------------------------------void AddrSpace::SaveState() {}//----------------------------------------------------------------------// AddrSpace::RestoreState// 	On a context switch, restore the machine state so that//	this address space can run.////      For now, tell the machine where to find the page table.//----------------------------------------------------------------------void AddrSpace::RestoreState() {    machine->pageTable = pageTable;    machine->pageTableSize = numPages;}