You need a copy of the rust sources to cross-compile libcore and
similar for the "new architecture" We have to do that because rustc
doesn't have a -m32. These sources need to be the same (or close
to), the sources used to build your rustc (see the commit hash in
rustc --version).
The Makefile looks for these sources at deps/rust , but you can
override that with make RUSTSRC=directory
The build is -O3 by default, but you can edit the Makefile to change
that. (Note, when debugging, you probably want -O1, since, with
rustc -O0 is "pessimized")
Run this by loading kernel/kernel.img and user/user.img into qemu
The kernel should be the first hard drive (hda).
The user program should be provided as the second hard drive (hdb).
The current recommended compiler/sources are 1.2 beta sources and nightly >= 2015-06-24
This code uses some unstable features (like inline assembly). To use
unstable features, you need a nightly build of the compiler. Since
tracking the nightly branch might be a bad idea, you can use
rustup.sh --channel=nightly --date=[date-of-relevant-beta-release]
to get as close to the beta build as possible. When you do that,
make sure to check out the corresponding source code. (rustup.sh,
which is Rust's installer script, also takes a --prefix option).