/**
* Transfer data from the specified array to this process's virtual memory. This method handles
* address translation details. This method must <i>not</i> destroy the current process if an
* error occurs, but instead should return the number of bytes successfully copied (or zero if no
* data could be copied).
*
* @param vaddr the first byte of virtual memory to write.
* @param data the array containing the data to transfer.
* @param offset the first byte to transfer from the array.
* @param length the number of bytes to transfer from the array to virtual memory.
* @return the number of bytes successfully transferred.
*/
public int writeVirtualMemory(int vaddr, byte[] data, int offset, int length) {
Lib.assertTrue(offset >= 0 && length >= 0 && offset + length <= data.length);
byte[] memory = Machine.processor().getMemory();
int transferred = 0;
while (length > 0 && offset < data.length) {
int addrOffset = vaddr % 1024;
int virtualPage = vaddr / 1024;
if (virtualPage >= pageTable.length || virtualPage < 0) {
break;
}
TranslationEntry pte = pageTable[virtualPage];
if (!pte.valid || pte.readOnly) {
break;
}
pte.used = true;
pte.dirty = true;
int physPage = pte.ppn;
int physAddr = physPage * 1024 + addrOffset;
int transferLength = Math.min(data.length - offset, Math.min(length, 1024 - addrOffset));
System.arraycopy(data, offset, memory, physAddr, transferLength);
vaddr += transferLength;
offset += transferLength;
length -= transferLength;
transferred += transferLength;
}
return transferred;
}
/**
* Read a null-terminated string from this process's virtual memory. Read at most <tt>maxLength +
* 1</tt> bytes from the specified address, search for the null terminator, and convert it to a
* <tt>java.lang.String</tt>, without including the null terminator. If no null terminator is
* found, returns <tt>null</tt>.
*
* @param vaddr the starting virtual address of the null-terminated string.
* @param maxLength the maximum number of characters in the string, not including the null
* terminator.
* @return the string read, or <tt>null</tt> if no null terminator was found.
*/
public String readVirtualMemoryString(int vaddr, int maxLength) {
Lib.assertTrue(maxLength >= 0);
byte[] bytes = new byte[maxLength + 1];
int bytesRead = readVirtualMemory(vaddr, bytes);
for (int length = 0; length < bytesRead; length++) {
if (bytes[length] == 0) return new String(bytes, 0, length);
}
return null;
}
/**
* Load the executable with the specified name into this process, and prepare to pass it the
* specified arguments. Opens the executable, reads its header information, and copies sections
* and arguments into this process's virtual memory.
*
* @param name the name of the file containing the executable.
* @param args the arguments to pass to the executable.
* @return <tt>true</tt> if the executable was successfully loaded.
*/
private boolean load(String name, String[] args) {
Lib.debug(dbgProcess, "UserProcess.load(\"" + name + "\")");
OpenFile executable = ThreadedKernel.fileSystem.open(name, false);
if (executable == null) {
Lib.debug(dbgProcess, "\topen failed");
return false;
}
try {
coff = new Coff(executable);
} catch (EOFException e) {
executable.close();
Lib.debug(dbgProcess, "\tcoff load failed");
return false;
}
// make sure the sections are contiguous and start at page 0
numPages = 0;
for (int s = 0; s < coff.getNumSections(); s++) {
CoffSection section = coff.getSection(s);
if (section.getFirstVPN() != numPages) {
coff.close();
Lib.debug(dbgProcess, "\tfragmented executable");
return false;
}
numPages += section.getLength();
}
// make sure the argv array will fit in one page
byte[][] argv = new byte[args.length][];
int argsSize = 0;
for (int i = 0; i < args.length; i++) {
argv[i] = args[i].getBytes();
// 4 bytes for argv[] pointer; then string plus one for null byte
argsSize += 4 + argv[i].length + 1;
}
if (argsSize > pageSize) {
coff.close();
Lib.debug(dbgProcess, "\targuments too long");
return false;
}
// program counter initially points at the program entry point
initialPC = coff.getEntryPoint();
// next comes the stack; stack pointer initially points to top of it
numPages += stackPages;
initialSP = numPages * pageSize;
// and finally reserve 1 page for arguments
numPages++;
if (!loadSections()) return false;
// store arguments in last page
int entryOffset = (numPages - 1) * pageSize;
int stringOffset = entryOffset + args.length * 4;
this.argc = args.length;
this.argv = entryOffset;
for (int i = 0; i < argv.length; i++) {
byte[] stringOffsetBytes = Lib.bytesFromInt(stringOffset);
Lib.assertTrue(writeVirtualMemory(entryOffset, stringOffsetBytes) == 4);
entryOffset += 4;
Lib.assertTrue(writeVirtualMemory(stringOffset, argv[i]) == argv[i].length);
stringOffset += argv[i].length;
Lib.assertTrue(writeVirtualMemory(stringOffset, new byte[] {0}) == 1);
stringOffset += 1;
}
return true;
}