LLVM failures cause exit status 1

[euclio]

Related to #51971.

If a fatal error occurs in LLVM, the compiler exits with status 1. This is problematic, because if a test is expecting a compilation failure, the test could still pass. It also makes it difficult to test for the presence of ICEs in general.

A simple fix would be to patch our copy of LLVM to exit with 101 (like ICEs) in report_fatal_error, but any other ideas would be appreciated.

[cuviper]

Those error functions all call sys::RunInterruptHandlers(), which sounds like it could be a great hook for us, but then that only calls RemoveFilesToRemove(). :/

[cuviper]

There is install_fatal_error_handler though, and that handler gets called first.

[euclio]

That sounds nice, but if we exit with 101 (or simply panic) in the handler won't we be skipping any other cleanup (sys::RunInterruptHandlers, plus any future cleanup that gets added there)? Or could we just call it in our handler?

I'm interested in putting a patch together, but I'm unfamiliar with how we link Rust to C++. The error handler needs to be able to consume a std::string.

[cuviper]

or simply panic

We shouldn't do anything that looks like exception unwinding. See install_fatal_error_handler:

  /// It is dangerous to naively use an error handler which throws an exception.
  /// Even though some applications desire to gracefully recover from arbitrary
  /// faults, blindly throwing exceptions through unfamiliar code isn't a way to
  /// achieve this.

won't we be skipping any other cleanup (sys::RunInterruptHandlers, plus any future cleanup that gets added there)? Or could we just call it in our handler?

I think we can call it -- it's publicly declared in llvm/Support/Signals.h. We might want to keep a note to make sure we check for new cleanup needed when we update LLVM though.

I'm interested in putting a patch together, but I'm unfamiliar with how we link Rust to C++. The error handler needs to be able to consume a std::string.

We bridge C++ code in src/rustllvm/. You could just write our handler in C++ there, and add some C-FFI function for librustc_codegen_llvm to call and hook that up.