Stable rustc always panics on arm/musl

[dragonmaus]

Stable rust is unable to compile anything on arm-unknown-linux-musleabihf (Raspberry Pi gen 1 running Void Linux).

Even a simple program like the following:

fn main() {
    println!("Hello, world!");
}

throws an "internal compiler error: unexpected panic" at "already borrowed: BorrowMutError".

Meta

rustc --version --verbose:

rustc 1.34.0
binary: rustc
commit-hash: unknown
commit-date: unknown
host: arm-unknown-linux-musleabihf
release: 1.34.0
LLVM version: 8.0

Backtrace:

thread 'rustc' panicked at 'already borrowed: BorrowMutError', src/libcore/result.rs:997:5
stack backtrace:
   0: <unknown>
   1: <unknown>
   2: <unknown>
   3: <unknown>
   4: <unknown>
   5: std::panicking::rust_panic_with_hook
   6: <unknown>
   7: rust_begin_unwind
   8: core::panicking::panic_fmt
   9: <unknown>
  10: syntax::attr::is_known
  11: <unknown>
  12: <unknown>
  13: <syntax::ext::expand::InvocationCollector<'a, 'b> as syntax::mut_visit::MutVisitor>::flat_map_item
  14: <unknown>
  15: <unknown>
  16: <unknown>
  17: <syntax::ext::expand::InvocationCollector<'a, 'b> as syntax::mut_visit::MutVisitor>::flat_map_item
  18: <unknown>
  19: <unknown>
  20: <unknown>
  21: syntax::ext::expand::MacroExpander::expand_crate
  22: <unknown>
  23: <unknown>
  24: <unknown>
  25: rustc_driver::driver::compile_input
  26: <unknown>
  27: <unknown>
  28: rustc_driver::run_compiler
  29: <unknown>
  30: __rust_maybe_catch_panic
  31: <unknown>
  32: <unknown>
  33: <unknown>
query stack during panic:
end of query stack

error: internal compiler error: unexpected panic

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: rustc 1.34.0 running on arm-unknown-linux-musleabihf

[mati865]

Probably not musl specific: #57665

@dragonmaus can you try with nightly? Hopefully it will have better debug info.

[dragonmaus]

@mati865 Rustup steadfastly refuses to work on this machine at all*, and -nightly is not available in the distro repositories, so I do not think I can be very helpful with that.

*The one from rustup.rs fails when it tries to run the rustup-init it downloads (with nothing more than a generic and information-free error message), and the one from the distro repositories complains as follows:

error: Pre-checks for host and toolchain failed: Provided host 'arm-unknown-linux-musleabihf' couldn't be converted to partial triple
If you are unsure of suitable values, the 'stable' toolchain is the default.
Valid host triples look something like: arm-unknown-linux-musleabihf

so I can make neither heads nor tails of it.

[pnkfelix]

triage: not sure what tier the given platform is, so I'm not assigning a priority to this yet. Leaving nominated for discussion.

[pietroalbini]

arm-unknown-linux-musleabihf is tier 2.

[nikomatsakis]

triage: P-high

Seems like a pretty important problem to get to the bottom of.

[pnkfelix]

nominating for discussion at meeting, hopefully to find someone with access to arm/musl to take this on.