Helpful hints

• The bulk of the changes you will make will be in exception.cc You will have to make changes to other files as well to support changes to these files. You may also need to create some new files/classes as your implementation demands. The design choices are completely up to you.

• Go through main.cc and system.cc in the threads directory to understand how Nachos starts up and executes user programs.

• If you are unclear about how to compile user programs for Nachos, look at the Makefile in the test directory. See how the sample user program halt is compiled.

• As we recommend for Lab 2, implement, compile, and test your program in small, manageable peices, instead of implementing everything and then compiling and testing.

• In order to test your implementation for exception handling, you will have to put some instructions in your user programs that you know will cause the kernel to raise an exception. Two examples are division by zero, integer overflow in addition or subtraction. You should put some code in your user program to cause the above to see how the kernel jumps to your exception handler and executes the code you place there.

• Read Section 4 in Thomas Narten's handout. If you haven't done so already, read Section 3.1 as well.

When you finish making changes to the file, compile in the usual way - type gmake depend and then gmake nachos to create a new executable. Note that the -x option provided by Nachos runs a user program on top of Nachos. You should use this option to test your system call implementation.