Mips (big endian) gives "undefined reference to `std::rt::lang_start'"

[jcowgill]

Attempting to compile this example program foo.rs using a nightly compiler:

fn main() {}

On a native mips big endian machine gives me this:

error: linking with `cc` failed: exit code: 1
  |
  = note: "cc" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-L" "/usr/local/lib/rustlib/mips-unknown-linux-gnu/lib" "foo.0.o" "-o" "foo" "-Wl,--gc-sections" "-pie" "-nodefaultlibs" "-L" "/usr/local/lib/rustlib/mips-unknown-linux-gnu/lib" "-Wl,-Bstatic" "/usr/local/lib/rustlib/mips-unknown-linux-gnu/lib/libstd-8bd0331885bb8f82.rlib" "/usr/local/lib/rustlib/mips-unknown-linux-gnu/lib/librand-c59b047c329fc869.rlib" "/usr/local/lib/rustlib/mips-unknown-linux-gnu/lib/libpanic_unwind-8b5a5d5d9b47b90e.rlib" "/usr/local/lib/rustlib/mips-unknown-linux-gnu/lib/libcollections-940fff481f9db1f7.rlib" "/usr/local/lib/rustlib/mips-unknown-linux-gnu/lib/liballoc-00bc69f25a7886ed.rlib" "/usr/local/lib/rustlib/mips-unknown-linux-gnu/lib/liballoc_system-8a70e0fa55025ef9.rlib" "/usr/local/lib/rustlib/mips-unknown-linux-gnu/lib/libunwind-6f736b1bf227d828.rlib" "/usr/local/lib/rustlib/mips-unknown-linux-gnu/lib/liblibc-0d4b94d34314ddab.rlib" "/usr/local/lib/rustlib/mips-unknown-linux-gnu/lib/libstd_unicode-27c6703fdb4bd5ba.rlib" "/usr/local/lib/rustlib/mips-unknown-linux-gnu/lib/libcore-f7c6aa272ea55579.rlib" "/usr/local/lib/rustlib/mips-unknown-linux-gnu/lib/libcompiler_builtins-93f6c14c48cd2162.rlib" "-Wl,-Bdynamic" "-l" "dl" "-l" "rt" "-l" "pthread" "-l" "gcc_s" "-l" "c" "-l" "m" "-l" "rt" "-l" "pthread" "-l" "util"
  = note: foo.0.o: In function `main':
          foo.cgu-0.rs:(.text.main+0x34): undefined reference to `std::rt::lang_start'
          collect2: error: ld returned 1 exit status


error: aborting due to previous error(s)

If I compile foo.rs to an object and dump the symbols, I see that the hash for lang_start is different between the object and the rlib file:

$ objdump -t foo.o | grep lang_start
00000000         *UND*  00000000 _ZN3std2rt10lang_start17h826655afc17b8ea3E

$ objdump -t /usr/local/lib/rustlib/mips-unknown-linux-gnu/lib/libstd-8bd0331885bb8f82.rlib | grep lang_start
00000000 l    d  .text._ZN3std2rt10lang_start17h5492aeb665e2d414E       00000000 .text._ZN3std2rt10lang_start17h5492aeb665e2d414E
00000000 g     F .text._ZN3std2rt10lang_start17h5492aeb665e2d414E       00000aec _ZN3std2rt10lang_start17h5492aeb665e2d414E

After some debugging, I managed to work out that the value of tcx.def_path_hash(def_id) for lang_start passed to the TypeIdHasher in rustc_trans::back::symbol_names::get_symbol_hash is byteswapped when run natively compared to running on an x86 -> mips cross compiler. I couldn't work out where this value originally comes from, but hopefully someone here knows. :)

I also tried using a stable compiler, but it failed with the issue #41471 before getting to this stage.

[est31]

cc @japaric

[arielb1]

I don't have a MIPS machine right here, but it certainly looks that def_path_hash should be returning a Fingerprint, which should be endianness-correct (i.e. return the same 2 u64s) - https://github.com/rust-lang/rust/blob/master/src/librustc/ich/fingerprint.rs#L68.

[arielb1]

@jcowgill

Does beta work, btw?

[jcowgill]

@arielb1
It looks like #41471 affects beta as well. I get the same error as on stable - this is with: rustc 1.18.0-beta.4 (0308c9865 2017-05-27)