Comment by jmkr | Hacker News Reader

Comment by jmkr | Hacker News Reader

Parent Full thread

Can you explain what that low hanging fruit is (or refer me to docs), and also explain it being a decision problem a bit more thoroughly. I will accept that if you have to run a program to decide if it's memory safe then that fits the criteria, but from my understanding static analysis doesn't run the program, and a compiler is parsing and lexing anyway so it should be able to catch at least some things (the low hanging fruit)?

Since I have actually started using C I realized how easy it is to be lazy and not handle memory right so it makes Rust and maybe C++ seem more appealing, but trying to figure out random segfaults it seems like address sanitizer and valgrind catches more than I would have assumed is a low hanging fruit.

I guess I should look more into how Rust manages that safety or understand what memory safety is trying to accomplish more formally. I've taken GC for granted for years until I needed to care about memory.

(Not your parent)

An example of low hanging fruit is -fwrapv. This flag takes a behavior that is undefined, signed overflow, and converts it to defined behavior, two's compliment wrapping. That improves safety, but it does not prevent all errors. There are many flags like this, but they all tackle individual aspects of the problem, and even if you turn them all on, there are situations which aren't caught.

Thanks. Yeah that makes sense for low hanging fruit. Going through the gcc flags it does seem like a lot of tradeoffs have to be made so you can't cover everything. A quick look through compiling Rust it seems it does at least some of this checking at MIR. I'll have to read more about it.

The compiler really doesn't have the opportunity to simulate every possibility of code. It's not just the matter of whether the function is safe, but every possible use of the function, which the compiler may not see when it is focused on a single compilation unit or a library.

If you want this level of safety, which is possible in C, then you need to use a model checker. Model checking C isn't as trivial as adding a flag to the compiler, but it can be done with about as much overhead as unit testing, if a reasonable idiomatic style is followed, and if the model checker is used well.

It is still a decision problem, and thus has similar limitations, but you can perform steps to ensure that you have some level of soundness with unwinding assertions and other techniques.

Thanks that's helpful I'll take a look at model checking.

Reply on news.ycombinator.com