asbestos

A toy OS, from scratch.

Goals and Non-Goals

I have the following goal for this project.

• Make an OS, "from scratch." We'll see what "from scratch" ends up meaning! (In 6.828, we implemented many parts of an OS, but it was not from scratch.)

The following are not goals for this project:

• Design a "good" OS. I intend to run this unstructured OS into the ground, first. Only then might I consider "doing it right" and designing an OS.

• Use other people's libraries wisely.. Making an OS from scratch is probably not a good idea. I would make progress a lot faster if I used other people's libraries. But, the from-scratch aspect is very important to me, so I'm declaring those libs to be off-limits.

Getting Asbestos

git clone https://github.com/jasonpr59/asbestos.git
# The rest of the README assumes that you are in the asbestos repository.
cd asbestos

Building Asbestos

Building the Toolchain

To build Asbestos, you'll need a cross-compilation toolchain targetting 'i686-elf'. By default, the Asbestos Makefile expects the toolchain to be installed in the cross directory (inside the top-level Asbestos directory). From within the Asbestos repo, install it with:

mkdir cross
cd toolchain
make install-binutils install-gcc install-libgcc DEST=../cross

# Finally, discard the downloaded source and intermediate build artificats.
# This does not touch installed artifacts.
make clean

# Return to top-level Asbestos directory for future steps.
cd ..

Building the kernel disk image

All of the Asbestos source combines to build asbestos.bin. This is a Multiboot-compatible disk image. Build it with:

make kernel

Running Asbestos

Running Asbestos in an emulator

I run Asbestos on QEMU. (On OS X, I installed QEMU with brew install qemu.)

Run QEMU using the asbestos.bin disk image with:

make qemu

Running Asbestos on real hardward

I've never tried this. Stay tuned for instructions.

Debugging Asbestos

Use GDB to debug Asbestos. asbestos.bin has file format elf32-i386. Your GDB might not understand that format. To install a "cross-GDB", do the following.

mkdir $ASBESTOS/toolchain/src
cd $ASBESTOS/toolchain/src
curl https://ftp.gnu.org/gnu/gdb/gdb-8.0.tar.xz > gdb.tar.xz
tar xf gdb.tar.xz -Cgdb --strip-components=1

mkdir $ASBESTOS/toolchain/build
cd $ASBESTOS/toolchain/build
$ASBESTOS/toolchain/src/gdb/configure --target=i686-elf --prefix=$ASBESTOS/cross
make
make install

After following the instructions above, you will have installed a "cross-GDB" in $ASBESTOS/cross/bin/i686-elf-gdb. Run QEMU with a GDB debug server with make qemu-gdb. Connect to it (from a separate shell) with make gdb (which uses the .gdbinit file in the root Asbestos directory to connect to the server and read the symbol file).