dynamic_lib::tests::test_loading_cosine fails on aarch64-unknown-linux-gnu

[chrisccoulson]

When running the tests for 1.20.0 on aarch64-unknown-linux-gnu (compiled on Ubuntu 17.10), I get the following failure:

---- dynamic_lib::tests::test_loading_cosine stdout ----                                                                                                                                                           
        thread 'dynamic_lib::tests::test_loading_cosine' panicked at 'Could not load function cos: /home/ubuntu/src/rustc/rust/build/aarch64-unknown-linux-gnu/stage1-rustc/aarch64-unknown-linux-gnu/release/deps/rustc_back-388893efdcf05f51: undefined symbol: cos', src/librustc_back/dynamic_lib.rs:129:30                                                                                                                       
note: Run with `RUST_BACKTRACE=1` for a backtrace.                                                                                                                                                                 
                                                                                                                                                                                                                   
                                                                                                                                                                                                                   
failures:                                                                                                                                                                                                          
    dynamic_lib::tests::test_loading_cosine                                                                                                                                                                        
                                                                                                                                                                                                                   
test result: FAILED. 72 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out

Despite the comment in src/librustc_back/dynamic_lib.rs "The math library does not need to be loaded since it is already statically linked in", this does not appear to be the case:

$ ldd build/aarch64-unknown-linux-gnu/stage1-rustc/aarch64-unknown-linux-gnu/release/deps/rustc_back-388893efdcf05f51
        linux-vdso.so.1 =>  (0x0000ffff9fef4000)
        libtest-5411e66a07bb6041.so => not found
        libsyntax-5e6bff834b4c594c.so => not found
        libserialize-5db2899038c5db44.so => not found
        libstd-f360fab4c9496629.so => not found
        libdl.so.2 => /lib/aarch64-linux-gnu/libdl.so.2 (0x0000ffff9fe5b000)
        libpthread.so.0 => /lib/aarch64-linux-gnu/libpthread.so.0 (0x0000ffff9fe2e000)
        libgcc_s.so.1 => /lib/aarch64-linux-gnu/libgcc_s.so.1 (0x0000ffff9fe0a000)
        libc.so.6 => /lib/aarch64-linux-gnu/libc.so.6 (0x0000ffff9fcb5000)
        /lib/ld-linux-aarch64.so.1 (0x0000ffff9fec9000)

My build uses all of the default options (including the vendored llvm).

I've not been able to verify whether this is an issue on master yet, because it fails during the build there.

[dezgeg]

NixOS has applied a patch to disable this test on aarch64 as well.

[cuviper]

Now this test is in librustc_metadata, but otherwise apparently unchanged. On Fedora, we get failures here on aarch64 and powerpc64le. On the rest of our platforms, readelf -d libtest-*.so shows that they are linked to libm.so.6, but not on aarch64 and powerpc64le. This is true of upstream rust binaries too.

I suspect the test doesn't really care about cosine at all. Perhaps it should exercise something more general, like from libc?