Awesome
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.