Fall 2006

Tools Used in 6.828

If you use the MIT Athena machines that run Linux, then all the software tools you will need for this course are located in the 6.828 locker: just type 'add 6.828' to get access to them. If you would like to compile and run the tools on your own machine, however, here is the information you need. Of course, we cannot guarantee that these tools will be portable to every possible machine you might want to run them on; they should at least compile easily on most recent versions of Linux, however.

It should be possible to get this development environment running under windows with the help of Cygwin. Install cygwin, and be sure to install the flex and bison packages (they are under the development header).

Compiler Toolchain

Most modern Linuxes and BSDs have an ELF toolchain compatible with the 6.828 labs. That is, the system-standard gcc, as, ld and objdump should just work. If your machine is in this camp, disable the i386-jos-elf- tool prefix in your make setup by adding the following line to conf/env.mk:


If you are in the minority and using something other than standard x86 linux or BSD, you will need the GNU C compiler toolchain, configured and built as a cross-compiler for the target 'i386-jos-elf'. You can download the specific versions we used via these links, although more recent versions of gcc and binutils should work too:

Once you've unpacked these archives, run the following commands as root:

$ cd binutils-2.15
$ ./configure --target=i386-jos-elf
$ make
$ make install
$ cd ../gcc-3.4.1
$ ./configure --target=i386-jos-elf
$ make
$ make install

If there are errors compiling gcc when it gets to libstdc++, don't worry about it.

Then you'll have in /usr/local/bin a bunch of binaries with names like i386-jos-elf-gcc. It will also be necessary to change the GNUMakefile used in the labs to use i386-jos-elf-gcc instead of gcc. There are instructions for how to do this inside of GNUMakefile.

Bochs Emulator

Bochs version 2.2.6 is set up on athena for x86 machines. If you want to use the same version on your home machine, you have two options.

  • Copy the binaries from athena. Run the following commands as root:
    cd /usr/local/bin
    scp <username>@athena.lcs.mit.edu:/afs/athena.mit.edu/course/6/6.828/arch/linux/bin/bochs .
    cd /usr/local/share
    scp -r <username>@athena.lcs.mit.edu:/afs/athena.mit.edu/course/6/6.828/share/bochs bochs 
  • The other option is to download, compile, and install bochs from the source archive. This is the only option if you want to run bochs under a different OS or on a different architecture. If you download a prebuilt version of bochs, it will not be compiled with the same options as we use for the class. Also, the Bochs version for the class contains a bug fix to make single-stepping work.

    We've prepared an automated, self-updating script to assist you in installing Bochs and potentially upgrading to new versions of Bochs. As root:

    # cd /some/tmp/build/dir
    # wget http://pdos.lcs.mit.edu/6.828/2006/src/bochs-install.sh
    # sh bochs-install.sh
    If we issue future updates to our 6.828 Bochs tarball, it would only be necessary to run:
    # cd /some/tmp/build/dir
    # sh bochs-install.sh
    Since the script asks our server what the most current version of the Bochs tarball is.

    To do things manually, fetch the 6.828-modified Bochs 2.2.6 source as follows:

    $ wget http://pdos.lcs.mit.edu/6.828/2006/src/bochs-2.2.6-6.828r1.tar.gz

    You may want to run ./configure --help and look at the available options, particularly --prefix= which determines where Bochs will be installed.

    tar xzvf bochs-2.2.6-6.828r1.tar.gz
    cd bochs-2.2.6-6.828r1
    ./configure --enable-disasm \
                --enable-smp \
                --enable-debugger \
                --enable-new-pit \
                --enable-all-optimizations \
                --enable-4meg-pages \
                --enable-global-pages \
                --enable-pae \
                --enable-all-optimizations \
                --disable-reset-on-triple-fault \
                --with-all-libs \
                --with-x \
                --with-x11 \
    make install
    For Mac OS X Tiger:
     ./configure --disable-cdrom --enable-disasm \
     --enable-debugger --enable-new-pit --enable-all-optimizations \
     --enable-4meg-pages --enable-global-pages --enable-pae \
     --enable-all-optimizations --disable-reset-on-triple-fault \
     --enable-smp --with-nogui --with-x11 --with-x --with-carbon

    If you wish to use a different UI than the default one, modify your .bochsrc file accordingly. See the bochsrc documentation. It should also be possible to just run man bochsrc.

    If you are compiling on a non-x86 platform or on windows, it may be necessary to remove the --enable-all-optimizations flag. If the make install step fails, it is probably possible to install it manually by copying ./bochs to /usr/bin/bochs and setting the environment variable BXSHARE to the path to the bochs-2.2.6 directory.

    If you want to use a different version of bochs (not recommended!), the 6.828-specific changes are in the bx_dbg_stepN_command function, in bx_debug/dbg_main.cc. The new function body looks like:

      void bx_dbg_stepN_command(bx_dbg_icount_t count)
        if (count == 0) {
          dbg_printf("Error: stepN: count=0\n");
        // use simulation mode while executing instructions.  When the prompt
        // is printed, we will return to config mode.
        // single CPU
        int old_guard = bx_guard.guard_for;
        bx_guard.guard_for |= BX_DBG_GUARD_ICOUNT; // looking for icount
        bx_guard.guard_for |= BX_DBG_GUARD_CTRL_C; // or Ctrl-C
        bx_guard.guard_for &= ~BX_DBG_GUARD_IADDR_ALL;
        // for now, step each CPU one instruction at a time
        for (unsigned cycle=0; cycle < count; cycle++) {
          for (unsigned cpu=0; cpu < BX_SMP_PROCESSORS; cpu++) {
    	    bx_guard.icount = 1;
            bx_guard.interrupt_requested = 0;
            int old_mode_break = BX_CPU(cpu)->mode_break;
            BX_CPU(cpu)->guard_found.guard_found = 0;
    		BX_CPU(cpu)->guard_found.icount = 0;
            BX_CPU(cpu)->mode_break = old_mode_break;
      #if BX_SUPPORT_SMP == 0
          // ticks are handled inside the cpu loop
        bx_guard.guard_for = old_guard;

Questions or comments regarding 6.828? Send e-mail to the TAs at 6.828-staff@pdos.csail.mit.edu.

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