Tachyon

Tachyon is a system for providing record, replay, and tandem execution by forwarding one process's system calls to the other.

This is still research quality code and is not extraordinarily stable.

Building

Tachyon's non-hackage dependencies are pointed to by git submodules. To pull them down, run

git submodule init
git submodule update

If you have Nix installed, you should just be able to run nix-build shell.nix to build. Otherwise, descend into each of ptrace and trace, running cabal install in each, then run cabal install in the root directory.

Usage

The Tachyon package provides two utilities: tracer and corediff.

Tracer

tracer can be invoked in 3 different modes: Record, Replay, and Tandem.

tracer RecordMode executable logfile

will record the stream of system calls made by executable to logfile.

Similarly,

tracer ReplayMode executable logfile

will execute executable using logfile as its system call stream source.

Finally,

tracer TandemMode exe1 exe2

will run exe1 and exe2 simultaneously, attempting to rewrite the system call from exe1 into something that exe2 can use.

Corediff

corediff allows you to diff cores generated when running the tracer process. This is primarily of interest for debugging in the case that replay is not proceeding as expected.

Caveats

This code is somewhat brittle, you may need to update or add features to get it to work on your particular kernel version/libc version etc. A good start if you notice unexpected deviations is to run corediff on cores you expect to be equal, and try to determine if any differences detected are problematic.

Threading is implemented by forcing system calls to interleave the same way on subsequent runs. This does not actually induce determinism, though it does come close. If you want to operate on threaded binaries in any kind of stable environment, I suggest you combine Tachyon with some sort of memory determinizer (e.g. dthreads).

If you have a specific problem, feel free to file an issue, and I'll try to look into it. However, this is not my current project, so any support is on a strictly best effort basis.