Cannot create rv64gc binary anymore since nightly-2019-05-10

[laanwj]

Here's a minimal reproduction: rv64gc-build-test.tar.gz

This works:

rustup toolchain install nightly-2019-05-09
rustup target  add riscv64gc-unknown-none-elf --toolchain nightly-2019-05-09
rustup toolchain install nightly-2019-05-10
rustup target  add riscv64gc-unknown-none-elf --toolchain nightly-2019-05-10

$ cargo +nightly-2019-05-09 build

This fails with a long linker error message:

$ cargo +nightly-2019-05-10 build

   Compiling rv64gc-build-test v0.1.0 (/home/user/rv64-build-test)
error: linking with `rust-lld` failed: exit code: 1
  |
  = note: "rust-lld" "-flavor" "gnu" "-L" "/home/user/.rustup/toolchains/nightly-2019-05-10-x86_64-unknown-linux-gnu/lib/rustlib/riscv64gc-unknown-none-elf/lib" "/home/user/rv64-build-test/target/riscv64gc-unknown-none-elf/debug/deps/rv64gc_build_test-ceeff793f013ca85.2n9gt1sqfhboah09.rcgu.o" "-o" "/home/user/rv64-build-test/target/riscv64gc-unknown-none-elf/debug/deps/rv64gc_build_test-ceeff793f013ca85" "--gc-sections" "-L" "/home/user/rv64-build-test/target/riscv64gc-unknown-none-elf/debug/deps" "-L" "/home/user/rv64-build-test/target/debug/deps" "-L" "/home/user/rv64-build-test/target/riscv64gc-unknown-none-elf/debug/build/rv64gc-build-test-6fe9523ab53da0fd/out" "-L" "/home/user/rv64-build-test/target/riscv64gc-unknown-none-elf/debug/build/riscv-74e5b865e4a295cf/out" "-L" "/home/user/rv64-build-test/target/riscv64gc-unknown-none-elf/debug/build/riscv-rt-7d092076a17d09e9/out" "-L" "/home/user/rv64-build-test/target/riscv64gc-unknown-none-elf/debug/build/riscv-rt-7d092076a17d09e9/out" "-L" "/home/user/.rustup/toolchains/nightly-2019-05-10-x86_64-unknown-linux-gnu/lib/rustlib/riscv64gc-unknown-none-elf/lib" "-Bstatic" "/home/user/rv64-build-test/target/riscv64gc-unknown-none-elf/debug/deps/libriscv_rt-9090a4f920915543.rlib" "/home/user/rv64-build-test/target/riscv64gc-unknown-none-elf/debug/deps/libr0-3c380a49758184f1.rlib" "/home/user/rv64-build-test/target/riscv64gc-unknown-none-elf/debug/deps/libriscv-42d4fa3f5d6ba30e.rlib" "/home/user/rv64-build-test/target/riscv64gc-unknown-none-elf/debug/deps/libbit_field-45876c749a94e638.rlib" "/home/user/rv64-build-test/target/riscv64gc-unknown-none-elf/debug/deps/libbare_metal-aa54f9169ec1e607.rlib" "--start-group" "/home/user/rv64-build-test/target/riscv64gc-unknown-none-elf/debug/deps/libpanic_halt-d30ee6629201fb4c.rlib" "/home/user/.rustup/toolchains/nightly-2019-05-10-x86_64-unknown-linux-gnu/lib/rustlib/riscv64gc-unknown-none-elf/lib/librustc_std_workspace_core-330c94737850f50a.rlib" "/home/user/.rustup/toolchains/nightly-2019-05-10-x86_64-unknown-linux-gnu/lib/rustlib/riscv64gc-unknown-none-elf/lib/libcore-2e0fb004fad6ca66.rlib" "--end-group" "/home/user/.rustup/toolchains/nightly-2019-05-10-x86_64-unknown-linux-gnu/lib/rustlib/riscv64gc-unknown-none-elf/lib/libcompiler_builtins-afe13c5355265d4c.rlib" "-Tmemory.x" "-Tlink.x" "-Bdynamic"
  = note: rust-lld: error: /home/user/.rustup/toolchains/nightly-2019-05-10-x86_64-unknown-linux-gnu/lib/rustlib/riscv64gc-unknown-none-elf/lib/libcompiler_builtins-afe13c5355265d4c.rlib(clzsi2.o) is incompatible with /home/user/rv64-build-test/target/riscv64gc-unknown-none-elf/debug/deps/rv64gc_build_test-ceeff793f013ca85.2n9gt1sqfhboah09.rcgu.o

error: aborting due to previous error

error: Could not compile `rv64gc-build-test`.

I do not yet know what causes this incompatibility.

[laanwj]

What is strange (to me) is that most of the objects in the referenced rlib are for X86-64, not RISC-V, this might be the source of the incompatibility:

$ readelf -a /home/user/.rustup/toolchains/nightly-2019-05-10-x86_64-unknown-linux-gnu/lib/rustlib/riscv64gc-unknown-none-elf/lib/libcompiler_builtins-afe13c5355265d4c.rlib|grep Machine
  Machine:                           RISC-V
  Machine:                           Advanced Micro Devices X86-64
  Machine:                           Advanced Micro Devices X86-64
... lots more

(I've checked and this is the case for all RISC-V 64 and 32 libcompiler_builtins libraries, for all versions I've looked at, even on stable, but apparently only today it started causing issues. It was not the case for AARCH64)

The object it's trying to link against, however, is RISC-V:

$ readelf -a /home/user/rv64gc-build-test/target/riscv64gc-unknown-none-elf/debug/deps/rv64gc_build_test-4cd742fb8def7147.xeu8wy2g6icc2av.rcgu.o | grep Machine:
  Machine:                           RISC-V

[mati865]

Does nightly-2019-05-10 work after running cargo clean (without running the older one)?

[laanwj]

Yes, this is not an issue with stale files: I even completely removed the target folder a few times.

[mati865]

Presumably rust-lang/compiler-builtins@752e35a

cc @alexcrichton

[alexcrichton]

Thanks for the report @laanwj and the cc @mati865, this should be fixed by rust-lang/compiler-builtins#291