paging-lc

A page table written in LC, based on the week 4 and week 5 labs from the Languages and Low-Level Programming Course(LLP). This lab was originally implemented in C, which can be found here.

To compile and run this program, you will need a copy of mil-tools. LC was intended to be used primarily as an intermediate language for the Habit compiler, which uses mil-tools as its back end and alb as its front end. The long term goal is to transition this example to a Habit implementation, which will give access to a broader range of language features and avoid some of the awkward details that can be expected from trying to create programs in an intermediate language that was not originally intended to be used for handwritten code. Nevertheless, we hope that the resulting code will be relatively easy to understand, and that it will help to give some indication of what will ultimately be possible using Habit.

Currently, only part of the week 4 lab has been implemented. A compilation error prevented further development. In its current state the program will compile and run, setting up a screen for the kernel and displaying various information. Uncommenting line 47 in paging-lc/kernel/kernel.llc will cause the compiler to throw a null pointer exception.

Installation Notes:

• The code in this repository assumes that you have installed mil-tools and added a copy of the milc script to a suitable folder on your path (for example, ~/bin/milc or ~/local/bin/milc). In addition, for the purposes of compiling these programs, you will need to modify that script to ensure that the mil-tools library folder (i.e., mil-tools/lib) is referenced when you run milc. This can be accomplished by editing the script file so that the second line matches the following pattern:

    java -jar MILPATH/mil-tools.jar -iMILPATH/lib $*
  

  where both occurrences of MILPATH are replaced with an absolute path for your mil-tools folder.

• We typically run these programs in a virtual machine that is running Ubuntu 18.04 LTS with the following packages installed:

    gcc make perl linux-headers-$(uname -r) \
    build-essential dkms clang llvm qemu xorriso libc6-x32 \
    parted default-jdk git ant gcc-multilib g++-multilib
  

  You can find a detailed set of instructions for building a virtual machine that is suitable for running these programs by clicking here. This information may also be useful if you are trying to configure a machine with a different version of Linux for the purpose of running these programs.

• We recommend using the provided Makefiles to compile and run these programs. For example, you can build a specific demo program using:

    make
  

  You can replace make with make run in either of the examples above to build and also run the program inside QEMU, or you can use make clean to remove temporary files that are generated during the build process.

libs-lc

This program depends on libraries that are packaged together in the libs-lc folder. (These are used in addition to the standard LC libraries in mil-tools/lib that provide more general functionality). The library files in libs-lc include:

• vram.llc: A simple video RAM library that includes functions for clearing the screen and writing data to screen.

• wvram.llc: An expanded version of vram.llc that supports the definition and use of multiple "windows" within the video RAM

• ia32.llc: A library of functions for working with low-level IA32 data structures, including contexts (for capturing CPU registers), and page tables and page directories for working with the MMU.

• cursor.llc: The beginnings of a general library for using "cursor" abstractions to traverse variable size data structures in a safe manner.

• mimg.llc: Functions for reading and displaying the bootdata information that is passed on by the mimg tool.

• portio.llc: Access to IA32 port IO, supported by the LLVM and assembly code fragments in portio.ll.

• pc-hardware.llc: Functions for working with the programmable interrupt controllers (PICs) and the programmable interval timer (PIT) on a standard PC platform.

• serial.llc: Functions for printing single characters, null-terminated strings, and numeric values on the COM1 serial port. When these demos are executed with the provided Makefile settings in QEMU, all output that is "printed on the serial port" will actually be displayed in the main terminal window. This can be useful for viewing and capturing program output, especially when there is too much to fit on a single video RAM screen.

• intervals.llc: Code for working with sets of intervals (that typically represent ranges of available or reserved memory addresses).