Com Sci 230
Operating Systems

Last modified: Mon Feb 26 11:40:40 CST 2001

NACHOS Source Code

Most of what you learn in this class you will learn by reading and modifying NACHOS source code. You need to become very familiar with the structure of that code, as early as possible. I haven't figured it out entirely myself, but I've noticed a few important points.

The Makefiles are to be designed to help organize the projects. They work with gmake, rather than make. Use these Makefiles all the time: don't even think of issuing your own compiler commands.
In order for the Makefiles to work properly, you need to use exactly the directory structure in which the source is now stored. To display that directory structure, I have provided a direct view of the files, as well as a more conceptually organized HTML presentation (under construction). You may also get at the source files directly through UNIX on the CS instructional system, outside of any WWW browser, at the path /usr/local/classes/current/CS230/01/Nachos/nachos-3.4/code.
The code directories appear to be organized, not according to the structure of the operating system, but according to the projects. Since these projects correspond fairly well to natural modules of the OS, that's not too bad for readability. But, some of the basic files are in the threads directory, not because they deal especially with threads/processes, but because the first project is concerned with threads. I am building an alternate HTML web displaying the OS structure more directly. Please post any errors that you discover in my organization to the online discussion immediately.
To complete your project work, you are allowed to change OS code, but not MIPS simulator code. All of the latter appears to be in the directory code/machine. Do not change any file in code/machine. code/threads/switch.s and code/threads/swtch.s contain machine-dependent code for context-switching. For your own peace of mind, don't change these either.

Guide to Reading the Source Code

Source Code

System Utilities

Debugging flags, ASSERT, miscellaneous arithmetic: code/threads/utility.h
code/threads/utility.cc
List manipulation: code/threads/list.h
code/threads/list.cc
Bitmap manipulation: User address spaces are bitmaps.
code/userprog/bitmap.h
code/userprog/bitmap.cc

Basic System Code

Bootstrap the kernel: code/threads/main.cc
Global system data, initialization, cleanup: code/threads/system.h
code/threads/system.cc

Threads

Representation of thread, fork, finish, yield, sleep operations: code/threads/thread.h
code/threads/thread.cc
Scheduler for threads: code/threads/scheduler.h
code/threads/scheduler.cc
Context switch: code/threads/switch.h
code/threads/switch.s (machine-dependent, do not modify)
Synchronization primitives (semaphores, locks, condition variables): code/threads/synch.h
code/threads/synch.cc
code/threads/synch.h-alt1 (ConditionVariables revised by Mike O'D)
code/threads/synch.cc-alt1 (ConditionVariables revised by Mike O'D)
code/threads/synch.cc-alt2 (Exchanger implemented with condition variables by Mike O'D.)
Synchronized list access: code/threads/synchlist.h
code/threads/synchlist.cc
code/threads/synchlist.cc-alt1 (ConditionVariables revised by Mike O'D)
Test program: two threads alternating: This test is executed by the system from the main function in code/threads/main.cc. It is not a user program.
code/threads/threadtest.cc
Test program: readers and writers with bounded buffer, by Mike O'D.: This test is intended to be executed by the system from the main function in code/threads/main.cc. In order to run it that way, you must make a small and obvious change to main. In order to compile it with the gmake command, you must modify code/threads/Makefile and code/Makefile.common. Use the treatment of threadtest.o/threadtest.cc as a model, and do the same things to buffertest.o/buffertest.cc.
code/threads/buffertest.cc
Test program: communication channel, by Mike O'D.: Analogous to the reader/writer test above.
code/threads/channeltest.cc
Test program: channel-buffer cycle, by Mike O'D.: Analogous to the reader/writer test above.
code/threads/chanbuftest.cc

User programs

Manage user address space: code/userprog/addrspace.h
code/userprog/addrspace.cc
Enter System from User Program (system call, exception, interrupt): code/userprog/syscall.h
code/userprog/exception.cc
Test programs: run user program or test console: One of the test functions StartProcess or ConsoleTest is executed by the system from the main function in code/threads.main.cc.
code/userprog/progtest.cc