[rustbuild] no entry fround for key during LLVM step when cross-compiling rustc

[nagisa]

$ python2 src/bootstrap/bootstrap.py --stage 2 --step rustc -j8 --target=i686-unknown-linux-gnu
    Finished debug [unoptimized + debuginfo] target(s) in 0.0 secs
Building stage0 std artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
    Finished release [optimized] target(s) in 0.0 secs
Building stage0 test artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
    Finished release [optimized] target(s) in 0.0 secs
Building stage0 compiler artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
    Finished release [optimized] target(s) in 0.0 secs
Building stage1 std artifacts (x86_64-unknown-linux-gnu -> i686-unknown-linux-gnu)
    Finished release [optimized] target(s) in 0.0 secs
Building stage1 test artifacts (x86_64-unknown-linux-gnu -> i686-unknown-linux-gnu)
    Finished release [optimized] target(s) in 0.0 secs
Building LLVM for i686-unknown-linux-gnu
thread 'main' panicked at 'no entry found for key', ../src/libcore/option.rs:700
stack backtrace:
   1:     0x561baf954479 - std::sys::backtrace::tracing::imp::write::h6f07380f45fe1307
   2:     0x561baf95c6dc - std::panicking::default_hook::_{{closure}}::he6993150602797ff
   3:     0x561baf95ba29 - std::panicking::default_hook::h42f7cdc1bed8dd00
   4:     0x561baf95c0e8 - std::panicking::rust_panic_with_hook::hdcce59947203a4c0
   5:     0x561baf95bf82 - std::panicking::begin_panic::h832a3d3207d44464
   6:     0x561baf95beb0 - std::panicking::begin_panic_fmt::hd1709f2e7b5289b9
   7:     0x561baf95be31 - rust_begin_unwind
   8:     0x561baf994aaf - core::panicking::panic_fmt::hdd0d476d63f35c21
   9:     0x561baf994b25 - core::option::expect_failed::hc4b6040e56029bcc
  10:     0x561baf6b93a6 - _<core..option..Option<T>>::expect::ha1df3f891b8f9b2d
                        at /buildslave/rust-buildbot/slave/beta-dist-rustc-linux/build/obj/../src/libcore/option.rs:294
  11:     0x561baf6a0ed7 - _<std..collections..hash..map..HashMap<K, V, S> as core..ops..Index<&'a Q>>::index::h7496f7eae83e9392
                        at /buildslave/rust-buildbot/slave/beta-dist-rustc-linux/build/obj/../src/libstd/collections/hash/map.rs:1218
  12:     0x561baf7964d5 - bootstrap::Build::cxx::h3205072a6636d676
                        at /home/nagisa/Documents/rust/rust/worktrees/more-cace/src/bootstrap/lib.rs:896
  13:     0x561baf7714a9 - bootstrap::native::llvm::h13c673c7ef1162af
                        at /home/nagisa/Documents/rust/rust/worktrees/more-cace/src/bootstrap/native.rs:103
  14:     0x561baf790891 - bootstrap::Build::build::he0c681db648efe1f
                        at /home/nagisa/Documents/rust/rust/worktrees/more-cace/src/bootstrap/lib.rs:253
  15:     0x561baf699593 - bootstrap::main::h1cf80230043bd02e
                        at /home/nagisa/Documents/rust/rust/worktrees/more-cace/src/bootstrap/bin/main.rs:36
  16:     0x561baf9641c6 - __rust_maybe_catch_panic
  17:     0x561baf95b192 - std::rt::lang_start::h14913182d401dec2
  18:     0x561baf699743 - main
  19:     0x7f283b969290 - __libc_start_main
  20:     0x561baf690729 - _start
  21:                0x0 - <unknown>

[alexcrichton]

Can you provide more assistance in debugging as well? For example what was at line 896 of lib.rs? What configuration did you provide? etc.

[nagisa]

Relevant line is a part of

/// Returns the path to the C++ compiler for the target specified, may panic
/// if no C++ compiler was configured for the target.
fn cxx(&self, target: &str) -> &Path {
    self.cxx[target].path()
}

At that point anything pertaining i686 in my config.toml were

target = [..., "i686-unknown-linux-gnu", ...]
# ...
[target.i686-unknown-linux-gnu]
# nothing here

Replacing [target.i686-unknown-linux-gnu] with

[target.i686-unknown-linux-gnu]
cc = "clang"
cxx = "clang++"

does still result in the same error.

---

For now, I just specified llvm-config for 32 bit version of LLVM I have, which works.

[alexcrichton]

Ah ok, thanks for the info!

Right now this should be a better error (of course) but the cause is how rustbuild treats the target and host arrays in the configuration. No C++ compilers are found for the target array, so you can't request any host-related targets (e.g. LLVM) when a triple is only mentioned in the target array. You can fix this by moving the target to the host array.