coffsection.java

nachos操作系统框架

// PART OF THE MACHINE SIMULATION. DO NOT CHANGE.

package nachos.machine;

import nachos.security.*;

import java.io.EOFException;
import java.util.Arrays;

/**
 * A <tt>CoffSection</tt> manages a single section within a COFF executable.
 */
public class CoffSection {
    /**
     * Allocate a new COFF section with the specified parameters.
     *
     * @param	coff		the COFF object to which this section belongs.
     * @param	name		the COFF name of this section.
     * @param	executable	<tt>true</tt> if this section contains code.
     * @param	readOnly	<tt>true</tt> if this section is read-only.
     * @param	numPages	the number of virtual pages in this section.
     * @param	firstVPN	the first virtual page number used by this.
     */
    protected CoffSection(Coff coff, String name, boolean executable,
			  boolean readOnly, int numPages, int firstVPN) {
	this.coff = coff;
	this.name = name;
	this.executable = executable;
	this.readOnly = readOnly;
	this.numPages = numPages;
	this.firstVPN = firstVPN;

	file = null;
	size = 0;
	contentOffset = 0;
	initialized = true;
    }
    
    /**
     * Load a COFF section from an executable.
     *
     * @param	file		the file containing the executable.
     * @param	headerOffset	the offset of the section header in the
     * 				executable.
     *
     * @exception	EOFException	if an error occurs.
     */
    public CoffSection(OpenFile file, Coff coff,
		       int headerOffset) throws EOFException {
	this.file = file;
	this.coff = coff;

	Lib.assert(headerOffset >= 0);
	if (headerOffset+headerLength > file.length()) {
	    Lib.debug(dbgCoffSection, "\tsection header truncated");
	    throw new EOFException();
	}
	
	byte[] buf = new byte[headerLength];
	Lib.strictReadFile(file, headerOffset, buf, 0, headerLength);
	
	name = Lib.bytesToString(buf, 0, 8);
	int vaddr = Lib.bytesToInt(buf, 12);
	size = Lib.bytesToInt(buf, 16);
	contentOffset = Lib.bytesToInt(buf, 20);
	int numRelocations = Lib.bytesToUnsignedShort(buf, 32);
	int flags = Lib.bytesToInt(buf, 36);

	if (numRelocations != 0) {
	    Lib.debug(dbgCoffSection, "\tsection needs relocation");
	    throw new EOFException();
	}

	switch (flags & 0x0FFF) {
	case 0x0020:
	    executable = true;
	    readOnly = true;
	    initialized = true;
	    break;
	case 0x0040:
	    executable = false;
	    readOnly = false;
	    initialized = true;
	    break;
	case 0x0080:
	    executable = false;
	    readOnly = false;
	    initialized = false;
	    break;
	case 0x0100:
	    executable = false;
	    readOnly = true;
	    initialized = true;
	    break;
	default:
	    Lib.debug(dbgCoffSection, "\tinvalid section flags: " + flags);
	    throw new EOFException();
	}

	if (vaddr%Processor.pageSize != 0 || size < 0 ||
	    initialized && (contentOffset < 0 ||
			    contentOffset+size > file.length())) {
	    Lib.debug(dbgCoffSection, "\tinvalid section addresses: " +
		      "vaddr=" + vaddr + " size=" + size +
		      " contentOffset=" + contentOffset);
	    throw new EOFException();
	}

	numPages = Lib.divRoundUp(size, Processor.pageSize);
	firstVPN = vaddr / Processor.pageSize;
    }

    /**
     * Return the COFF object used to load this executable instance.
     *
     * @return	the COFF object corresponding to this section.
     */
    public Coff getCoff() {
	return coff;
    }

    /**
     * Return the name of this section.
     *
     * @return	the name of this section.
     */
    public String getName() {
	return name;
    }

    /**
     * Test whether this section is read-only.
     *
     * @return	<tt>true</tt> if this section should never be written.
     */
    public boolean isReadOnly() {
	return readOnly;
    }

    /**
     * Test whether this section is initialized. Loading a page from an
     * initialized section requires a disk access, while loading a page from an
     * uninitialized section requires only zero-filling the page.
     *
     * @return	<tt>true</tt> if this section contains initialized data in the
     *		executable.
     */
    public boolean isInitialzed() {
	return initialized;
    }

    /**
     * Return the length of this section in pages.
     *
     * @return	the number of pages in this section.
     */
    public int getLength() {
	return numPages;
    }

    /**
     * Return the first virtual page number used by this section.
     *
     * @return	the first virtual page number used by this section.
     */
    public int getFirstVPN() {
	return firstVPN;
    }

    /**
     * Load a page from this segment into physical memory.
     *
     * @param	spn	the page number within this segment.
     * @param	ppn	the physical page to load into.
     * @return	<tt>true</tt> if successful.
     */
    public void loadPage(int spn, int ppn) {
	Lib.assert(file != null);
	
	Lib.assert(spn>=0 && spn<numPages);
	Lib.assert(ppn>=0 && ppn<Machine.processor().getNumPhysPages());

	int pageSize = Processor.pageSize;
	byte[] memory = Machine.processor().getMemory();
	int paddr = ppn*pageSize;
	int faddr = contentOffset + spn*pageSize;
	int initlen;

	if (!initialized)
	    initlen = 0;
	else if (spn == numPages-1)
	    initlen = size % pageSize;
	else
	    initlen = pageSize;

	if (initlen > 0)
	    Lib.strictReadFile(file, faddr, memory, paddr, initlen);

	Arrays.fill(memory, paddr+initlen, paddr+pageSize, (byte) 0);
    }

    /** The COFF object to which this section belongs. */
    protected Coff coff;
    /** The COFF name of this section. */
    protected String name;
    /** True if this section contains code. */
    protected boolean executable;
    /** True if this section is read-only. */
    protected boolean readOnly;
    /** True if this section contains initialized data. */
    protected boolean initialized;

    /** The number of virtual pages in this section. */
    protected int numPages;
    /** The first virtual page number used by this section. */
    protected int firstVPN;

    private OpenFile file;
    private int contentOffset, size;
    
    /** The length of a COFF section header. */
    public static final int headerLength = 40;

    private static final char dbgCoffSection = 'c';
}