Unsupported crate type results in ICE

[hellow554]

rustc --version; cat lib.rs; env RUST_BACKTRACE=1 rustc --emit asm lib.rs --crate-type dylib -O --target thumbv7em-none-eabihf
rustc 1.28.0-nightly (cb20f68d0 2018-05-21)
#![no_std]
pub fn pete() -> u32 {
        2
}
warning: dropping unsupported crate type `dylib` for target `thumbv7em-none-eabihf`

thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', libcore/option.rs:335:21
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::print
             at libstd/sys_common/backtrace.rs:71
             at libstd/sys_common/backtrace.rs:59
   2: std::panicking::default_hook::{{closure}}
             at libstd/panicking.rs:211
   3: std::panicking::default_hook
             at libstd/panicking.rs:227
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:467
   6: std::panicking::begin_panic_fmt
             at libstd/panicking.rs:350
   7: rust_begin_unwind
             at libstd/panicking.rs:328
   8: core::panicking::panic_fmt
             at libcore/panicking.rs:71
   9: core::panicking::panic
             at libcore/panicking.rs:51
  10: rustc_codegen_llvm::base::write_metadata
  11: rustc::util::common::time
  12: rustc_codegen_llvm::base::codegen_crate
  13: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_utils::codegen_backend::CodegenBackend>::codegen_crate
  14: rustc::util::common::time
  15: rustc_driver::driver::phase_4_codegen
  16: rustc_driver::driver::compile_input::{{closure}}
  17: rustc::ty::context::tls::enter_context
  18: <std::thread::local::LocalKey<T>>::with
  19: rustc::ty::context::TyCtxt::create_and_enter
  20: rustc_driver::driver::compile_input
  21: rustc_driver::run_compiler_with_pool
  22: syntax::with_globals
  23: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  24: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:105
  25: rustc_driver::run
  26: rustc_driver::main
  27: std::rt::lang_start::{{closure}}
  28: std::panicking::try::do_call
             at libstd/rt.rs:59
             at libstd/panicking.rs:310
  29: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:105
  30: std::rt::lang_start_internal
             at libstd/panicking.rs:289
             at libstd/panic.rs:374
             at libstd/rt.rs:58
  31: main
  32: __libc_start_main
  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 1.28.0-nightly (cb20f68d0 2018-05-21) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type dylib

[hellow554]

This does not happen on either stable or beta, only nightly.

[nikomatsakis]

@hellow554 if it's easy for you, any chance you could bisect with this tool?

https://github.com/rust-lang-nursery/cargo-bisect-rustc

That would help us pinpoint precisely what introduced the fault. But this is presumably a simple fix...

[hellow554]

Sorry, i was a little bit too sloppy.
On stable it does not crash, but just because stable does not know the target thumv7em-none-eabi.
Beta does indeed crash as well on the same error.
I think #51035 will fix the problem, let's see. Hadn't time to do a bisect yet

[oli-obk]

Oh... this might be a new bug entiretly then. Most likely a bisection would point to the PR that added said targets

[hellow554]

I can confirm, that your patch fixes the ICE :) thanks @oli-obk .

The question is, what is it supposed to do now. I creates a .s file, but it remains mostly empty (so no assembly is generated for that function). Is that what it is supposed to do?

[oli-obk]

I have no idea. Is that problematic?

[hellow554]

Not at all, I'm just curious to know.