/**
* Handle a syscall exception. Called by <tt>handleException()</tt>. The <i>syscall</i> argument
* identifies which syscall the user executed:
*
* <table>
* <tr><td>syscall#</td><td>syscall prototype</td></tr>
* <tr><td>0</td><td><tt>void halt();</tt></td></tr>
* <tr><td>1</td><td><tt>void exit(int status);</tt></td></tr>
* <tr><td>2</td><td><tt>int exec(char *name, int argc, char **argv);
* </tt></td></tr>
* <tr><td>3</td><td><tt>int join(int pid, int *status);</tt></td></tr>
* <tr><td>4</td><td><tt>int creat(char *name);</tt></td></tr>
* <tr><td>5</td><td><tt>int open(char *name);</tt></td></tr>
* <tr><td>6</td><td><tt>int read(int fd, char *buffer, int size);
* </tt></td></tr>
* <tr><td>7</td><td><tt>int write(int fd, char *buffer, int size);
* </tt></td></tr>
* <tr><td>8</td><td><tt>int close(int fd);</tt></td></tr>
* <tr><td>9</td><td><tt>int unlink(char *name);</tt></td></tr>
* </table>
*
* @param syscall the syscall number.
* @param a0 the first syscall argument.
* @param a1 the second syscall argument.
* @param a2 the third syscall argument.
* @param a3 the fourth syscall argument.
* @return the value to be returned to the user.
*/
public int handleSyscall(int syscall, int a0, int a1, int a2, int a3) {
switch (syscall) {
case syscallHalt:
return handleHalt();
case syscallCreate:
return handleCreate(a0);
case syscallOpen:
return handleOpen(a0);
case syscallRead:
return handleRead(a0, a1, a2);
case syscallWrite:
return handleWrite(a0, a1, a2);
case syscallClose:
return handleClose(a0);
case syscallUnlink:
return handleUnlink(a0);
case syscallExit:
handleExit(a0);
case syscallExec:
return handleExec(a0, a1, a2);
case syscallJoin:
return handleJoin(a0, a1);
default:
Lib.debug(dbgProcess, "Unknown syscall " + syscall);
Lib.assertNotReached("Unknown system call!");
}
return 0;
}
/**
* Initializes page tables for this process so that the executable can be demand-paged.
*
* @return <tt>true</tt> if successful.
*/
protected boolean loadSections() {
UserKernel.memoryLock.acquire();
pageTable = new TranslationEntry[numPages];
for (int vpn = 0; vpn < numPages; vpn++) {
pageTable[vpn] = new TranslationEntry(vpn, -1, false, false, false, false);
}
UserKernel.memoryLock.release();
// load sections
for (int s = 0; s < coff.getNumSections(); s++) {
CoffSection section = coff.getSection(s);
Lib.debug(
dbgProcess,
"\tinitializing " + section.getName() + " section (" + section.getLength() + " pages)");
for (int i = 0; i < section.getLength(); i++) {
int vpn = section.getFirstVPN() + i;
pageTable[vpn].readOnly = section.isReadOnly();
// section.loadPage(i, pinVirtualPage(vpn, false));
}
}
return true;
}
/**
* Allocates memory for this process, and loads the COFF sections into memory. If this returns
* successfully, the process will definitely be run (this is the last step in process
* initialization that can fail).
*
* @return <tt>true</tt> if the sections were successfully loaded.
*/
protected boolean loadSections() {
if (numPages > Machine.processor().getNumPhysPages()) {
coff.close();
Lib.debug(dbgProcess, "\tinsufficient physical memory");
return false;
}
pageTable = new TranslationEntry[numPages];
for (int i = 0; i < numPages; i++) {
int physPage = UserKernel.allocatePage();
if (physPage < 0) {
Lib.debug(dbgProcess, "\tunable to allocate pages; tried " + numPages + ", did " + i);
for (int j = 0; j < i; j++) {
if (pageTable[j].valid) {
UserKernel.deallocatePage(pageTable[j].ppn);
pageTable[j].valid = false;
}
}
coff.close();
return false;
}
pageTable[i] = new TranslationEntry(i, physPage, true, false, false, false);
}
// load sections
for (int s = 0; s < coff.getNumSections(); s++) {
CoffSection section = coff.getSection(s);
Lib.debug(
dbgProcess,
"\tinitializing " + section.getName() + " section (" + section.getLength() + " pages)");
for (int i = 0; i < section.getLength(); i++) {
int vpn = section.getFirstVPN() + i;
// for now, just assume virtual addresses=physical addresses
int ppn = pageTable[vpn].ppn;
section.loadPage(i, ppn);
if (section.isReadOnly()) {
pageTable[vpn].readOnly = true;
}
}
}
coff.close();
return true;
}
/**
* 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.exceptionSyscall:
int result =
handleSyscall(
processor.readRegister(Processor.regV0),
processor.readRegister(Processor.regA0),
processor.readRegister(Processor.regA1),
processor.readRegister(Processor.regA2),
processor.readRegister(Processor.regA3));
processor.writeRegister(Processor.regV0, result);
processor.advancePC();
break;
default:
Lib.debug(dbgProcess, "Unexpected exception: " + Processor.exceptionNames[cause]);
handleExit(-1);
Lib.assertNotReached("Unexpected exception");
}
}
/**
* 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;
}