backtraces have blank lines and <unknown> instead of function names on FreeBSD

[umanwizard]

Note that I am using rustup, not the FreeBSD lang/rust port.

$ cat test.rs
fn main() {
    panic!();
}
$ rustc test.rs && RUST_BACKTRACE=1 ./test                                                                                        
thread 'main' panicked at 'explicit panic', test.rs:2:5
stack backtrace:
   0: <std::thread::local::AccessError as core::fmt::Debug>::fmt
   1: <std::ffi::c_str::NulError as core::fmt::Debug>::fmt
   2: <std::ffi::c_str::NulError as core::fmt::Debug>::fmt
   3: <std::ffi::c_str::NulError as core::fmt::Debug>::fmt
   4: <std::ffi::c_str::NulError as core::fmt::Debug>::fmt
   5: 
   6: 
   7: 
   8: <std::ffi::c_str::NulError as core::fmt::Debug>::fmt
   9: <std::ffi::c_str::NulError as core::fmt::Debug>::fmt
  10: 
  11: 
  12: 
  13: 
  14: <unknown>
$ rustc --version --verbose
rustc 1.29.0 (aa3ca1994 2018-09-11)
binary: rustc
commit-hash: aa3ca1994904f2e056679fce1f185db8c7ed2703
commit-date: 2018-09-11
host: x86_64-unknown-freebsd
release: 1.29.0
LLVM version: 7.0
$ freebsd-version
11.2-RELEASE-p3

[umanwizard]

Output for the same code on macOS -- notice that test::main appears on frame 6, as expected.

~ ❯❯❯ RUST_BACKTRACE=1 ./test                                            ✘ 101 
thread 'main' panicked at 'explicit panic', test.rs:2:5
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
   1: std::sys_common::backtrace::print
   2: std::panicking::default_hook::{{closure}}
   3: std::panicking::default_hook
   4: std::panicking::rust_panic_with_hook
   5: std::panicking::begin_panic
   6: test::main
   7: std::rt::lang_start::{{closure}}
   8: std::panicking::try::do_call
   9: __rust_maybe_catch_panic
  10: std::rt::lang_start_internal
  11: std::rt::lang_start
  12: main

[estebank]

There's a downstream patch for this https://reviews.freebsd.org/D11574 (found through https://svnweb.freebsd.org/ports/head/lang/rust/files/)

Upstreamed path to gcc: https://gcc.gnu.org/ml/gcc-patches/2018-03/msg00068.html (don't know how to tell if it's been merged)

[tromey]

Upstreamed path to gcc: https://gcc.gnu.org/ml/gcc-patches/2018-03/msg00068.html (don't know how to tell if it's been merged)

I looked at gcc git and that patch is not there. It also isn't in https://github.com/ianlancetaylor/libbacktrace (I'm not sure anymore if one repository is canonical or if merges are done both ways).

[umanwizard]

By the way, mounting /proc fixes this. But mounting /proc is considered a Linuxism so it would be best if this weren't necessary on FreeBSD.

[tromey]

I'd suggest sending the patch as a PR to the aforementioned libbacktrace repository, then once it lands, also update the libbacktrace in rust-lang-nursery.