Re:Impact of Undefined Behavior on Performance
by MichaelBurge on Friday July 09, 2021 @10:55AM
(#27784325)
Undefined behavior applies internally to the language's code, not to foreign code. FFIs specify how the compiler is to invoke foreign code, how to prepare any arguments, and how to handle any return values. They are not typically part of the language standard, but rather the OS standard.
Windows has different requirements for invoking foreign code vs. Linux for example.
The foreign code may have requirements on how it should be called, but it is not C's undefined behavior to invoke an OS system call incorrectly because the OS is not regulated by the C standard.
You can formally prove that a program has no undefined behavior, and it can still have lots of errors when actually run.
If this is true, then this should also apply to Rust or other proven languages: your program will still run in a dynamic environment, and probably calling into all kind of OS and third party libraries. Unless... you write your own (unsafe) wrappers around libraries, trying to catch, as much as possible, errors that can filter into the Rust (or whatever) code. But still, someone has to write these wrappers. If it's not you, you have to trust on somebody else's work, and this is a runtime check that will slow your program down.