Name collision between extern "C" functions can cause undefined behavior in safe code

[dgrunwald]

I'm generating extern "C" functions using macros. Since it's currently not possible to use $concat_ident for function names, I can't give these functions unique names.

I was hoping for rust's name mangling to take care of the issue; but unfortunately this doesn't work if the macro is used twice in the same function. This usually results in internal compiler errors for me, but on the playpen machine it's possible to produce undefined behavior in safe code:

fn main() {
    {
        extern "C" fn test(a: &mut i32) {
            println!("a: {:?}", a);
            *a = 1;
        }
    }
    {
        extern "C" fn test(b: &i32) {
            println!("b: {:?}", b);
        }
        test(&1);
    }
}

Expected output: b: 1
Actual output: a: 1
playpen: application terminated abnormally with signal 4 (Illegal instruction)

[alexcrichton]

Hm this sounds like a bug, the compiler should be giving each of these extern functions a different symbol...

[nagisa]

On the nightlies it is an ICE:

error: internal compiler error: symbol `_ZN4main4test10__rust_abiE` already defined
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
note: run with `RUST_BACKTRACE=1` for a backtrace

[ruuda]

Not sure if it is the same bug, but this also ICEs rustc 1.1.0-nightly (7bd71637c 2015-05-06) (built 2015-05-06):

fn main() {}

mod foo {
    extern {
        fn main();
    }
}

[mattico]

I believe I'm having the same issue with nightly-2016-02-22. I posted a backtrace over here SkylerLipthay/interpolate_idents#7 and I'll be trying to debug this sometime soon. Unless the issue is very simple I won't have the ability to fix it, but I should be able to identify what the problem is.

[dgrunwald]

Closing in favor of #26201, that issue has a more up-to-date title.