Issue building 'Setup Rust'

[RyanPSullivan]

Hey Im experiencing the following error when trying to build at the end of the setup rust tutorial

target/x86_64-unknown-linux-gnu/debug/librust_os.a(core-1357b93f.0.o): In function core::panicking::panic_fmt': /buildslave/rust-buildbot/slave/nightly-dist-rustc-linux/build/obj/../src/libcore/panicking.rs:69: undefined reference to rust_begin_unwind'

[RyanPSullivan]

Ah I've seen that you already raised the issue on the rust-lang page rust-lang/rust#38281 and they posted a solution that seems to work,

[phil-opp]

Thanks for reporting!

Yeah, this is a rust problem that was introduced in the 2016-12-05 nightly: rust-lang/rust#38281. It seems like the panic_fmt lang item doesn't export the rust_begin_unwind symbol anymore.

I know of two workarounds:

1. Use the 2016-12-04 nightly until the issue is resolved.
2. Define a exported rust_begin_unwind symbol in the assembly sources. However, with this approach rust will jump to the assembly symbol on panic, which isn't desirable.

[adeadman]

I left a comment on the blog post DIsqus, but you don't need to export that symbol in the sources. Just add #[no_mangle] to the panic_fmt entry like so:
#[lang = "panic_fmt"] #[no_mangle] pub extern fn panic_fmt() -> ! {loop{}}

This compiles and runs without error.

[phil-opp]

Thanks a lot for the hint! It works without problems.

I added no_mangle to all panic_fmt declarations in #262.

[phil-opp]

It seems like pub + no_mangle is the official solution now.

I've updated the source code and all posts and cherry-picked the changes to all tags. So I think this issue is resolved.