Hard for humans. But it's DARPA, is it hard for AI? Image classification used to be hard also, today cars drive themselves.
I'd say it's good timing.
I'd say it's good timing.
You can attach about a hundred asterisks to that.
If anything, I think self the failure to hit L5 driving after billions of dollars and millions of man hours invested is probably reflective of how automatic C to Rust translation will go. We'll cruise 90% of the way, but the last 10% will prove insurmountable with current technology.
Think about the number of C programs in the wild that rely on compiler-specific or libc-specific or platform-specific behavior, or even undefined behavior plus the dumb luck of a certain brittle combination of {compiler version} ∩ {libc version} ∩ {linker version} ∩ {build flags} emitting workable machine code. There's a huge chunk of C software where there's not enough context within the source itself (or even source plus build scripts) to understand the behavior. It's not even clear that this is a solvable problem in the abstract.
None of that is to say that DARPA shouldn't fund this. Research isn't always about finding an industrial strength end product; the knowledge and expertise gained along the way is important too.
Even if it's "can handle well 90%" of the transition for any project, this is still interesting. Unlike cars on the road, most code transition project out there doesn't need to be 100% fine to provide some useful value.
Just getting something vaguely Rust shaped which can compile is the first step in overcoming the inertia to leave the program in its current language.
There is real utility in slowly fleshing out the number of transforms in a tool like c2rust that can recognise high-level constructs in C code and produce idiomatic safe equivalents in rust
It'll be great for "pure" functions. For the grimey parts of the world, funcs taking pointer args and returning pointers, for things that access and modify global data without locks, for threaded code with implicit (and undocumented) locking, the tool would add most value. If it can. Even only by saying "this code looks grimey. here's why. A bit of FFI will also be thrown in because it links against 100 libraries. I suggest changes along those lines ... use one of the 2000000 hint flags to pick-your-evil".
> You can attach about a hundred asterisks to that.
Not in San Francisco. There are about 300 Waymo cars safely driving in one of the most difficult urban environments around (think steep hills, fog, construction, crazy traffic, crazy drivers, crazier pedestrians). Five years ago this was "someday" science-fiction. Frankly I trust them much more then human drivers and envision a future utopia where human drivers are banned from urban centers.
To get back on topic, I don't think automatic programming language translation is nearly as hard, especially since we have a deterministic model of the machines it runs on. I can see a possible approach where AI systems take the assembler code of a C++ program, then translate that into Rust, or anything else. Can they get 100% accuracy and bit-for-bit compatibility on output? I would not bet against it.
Getting identical outputs on safe executions, catching any unsafe behavior (at translation-time or run-time), and producing efficient, maintainable code all at once is a million times harder.
In 10 (or 2 or 50 or X) years when Chevy, Ford, and others are rolling out cheap self driving this argument stops working. The important thing is that this argument stops working with no change in how hard C to Rust conversion is.
We really should be looking at the specifics of both problems. What makes computer language translation hard? Why is driving hard? One needs to be correct while inferring intent and possibly reformulating code to meet new restrictions. The other needs to be able to make snap judgments and in realtime avoid hitting things even if it just means stopping to prefer safety over motion. One problem can be solved piecewise without significant regard to time and the other solved in realtime as it happens without producing unsafe output.
These problems really aren't analogous.
I think you picked self driving cars just because it is a big and only partially solved problem. One could just as easily pick a big solved problem or a big unstarted problem and formulate equally bad arguments.
I am not saying this problem is easy, just that it seems solvable with sufficient effort.
I'd put money on the solutions to said problems looking largely the same though - big ass machine learning models.
My prediction is that a tool like copilot (but specialized to this domain) will do the bulk of source code conversions, with a really smart human coming behind to validate.
The director orders the use of the tool when the dev team got downsized (and the two most-seniors left for greener pastures just after that). Validation is in the "extensive" tests anyway, we have those, right, so the new intern shall have a look, make it all work (fudge the tests where possible and remove the persistently failing ones as they've probably been always broken). The salesman said it comes from the DOA or DOD or something. If the spooks can do it so can we.
Which are things that took 20 or 50 years longer than expected in some cases.
> I think you picked self driving cars just because it is a big and only partially solved problem. One could just as easily pick a big solved problem or a big unstarted problem and formulate equally bad arguments.
But C to Rust translation is a big and only partially solved problem.
But, this isn't just about rewriting code from one language to another. It's about reverse engineering complex information out of the code, which may not be immediately visible in it, and then finding a way to make it "safe" according to Rust's type system. Where's the training data for that? It'd be really hard even for skilled humans.
Personally I think the most pragmatic way to make C/C++ memory safe quicker is one of two approaches:
1. Incrementally. Make std::vector[] properly bounds checked (still not done even in chrome!), convert allocations to allocations that know their own size and do bounds checking e.g. https://issues.chromium.org/issues/40285824
2. Or, go the whole hog and use runtime techniques like garbage collection and runtime bounds checks.
A good example of approach (2) is Managed Sulong, which extends the JVM to execute LLVM bitcode directly whilst exposing to the C/C++/FORTRAN a virtualized Linux syscall interface. The whole piece of code can be sandboxed with permissions, and memory safety errors are caught at runtime. The compiler tries to optimize out as many bounds checks as possible. The interesting thing about this approach is it doesn't require big changes to the source code (as long as it's already been ported to Linux), which means the work of making something safe can be done by teams independent of the original authors. In practice "rewrite it in Rust" will usually mean a fork, which introduces lots of complicated technical, cultural and economic issues.
Managed Sulong is also a research project and has a bunch of problems to solve, for instance it needs to lose the JITC dependency and go fully AOT compiled (doable, there's no theoretical issue with it and much of the needed infra already exists). And performance/memory usage can always be improved of course, it regresses vs the original C. But those are "just" systems engineering problems, not rewrite-the-world and solve-static-analysis problems.
Disclosure: I do work part time at Oracle Labs which developed Managed Sulong, but I don't work on it.
Microsoft has this:
https://learn.microsoft.com/en-us/cpp/standard-library/safe-...
but it doesn't seem to actually make std::vector[] safe.
It's frustrating that low hanging fruit like this doesn't get harvested.
[1] "although there are precondition checks for some string operations, e.g. operator[], they will not always be run when using the char and wchar_t specializations (std::string and std::wstring)."
https://github.com/microsoft/STL/issues/586
> We talked about this at the weekly maintainer meeting and decided that we're not comfortable enough with the (lack of) design of this feature to begin documenting it for wide usage.
I tried a toy example with GCC [1], Clang [2], and MSVC [3], and none of them emit bounds checks with basic optimization flags.
[1] https://godbolt.org/z/W5e3n5oWM
That might not be too bad.
A combination of a formal system and an LLM might work here. Suppose we see a C function
void somefn(char* buf, int n);
If it's an array, how big is it? We don't have enough info to know that yet. But a reasonable guess, and one than an LLM might make, is that the length of buf is "n".
Following that assumption, it's reasonable to translate this to Rust as
fn somefn(buf: &[u8])
buf.len()
assert!(buf.len() == n);
somefn(buf, n);
fn somefn(buf: &[u8], int n)
The idea is to recognize common C idioms and do clean translations to Rust for them. This should handle a high percentage of cases.
But if you're going to do it that way, the right place to start is probably to a safer form of C++ not Rust. That way code can be ported file-at-a-time or even function-at-a-time, and so you'll have a chance to run the assertions in the context of the original code. Which of course may not have good test coverage, as C codebases often don't, so you'll have to be testing your assertions in production.
There's something to be said for that. You're going to need at least an internal representation that's a safe C/C++.
Most compilers do have flags to turn this on, which I use all the time.
The issue is the "performance trumps safety" culture that pushes back against using them.
This is an excellent example of government action I like to see, as it isn't about favoritism or the swamp dynamics. Just provide a target, a bounty and no or low barriers to entry.
This challenge does push Rust out in front of everybody. That's a mixed blessing. I hope this challenge gets modified to not specify the target language, but instead the requirement of memory and type safety. Rust is likely an intermediate stop on the way to something better, and it shouldn't matter if that language is called Rust 2.0 or something else.