llvm error: Relocation not implemented yet! when running RxCpp in orcjit or lli

Question

I would like to run RxCpp example in llvm's IR interpreter lli.

Unfortunately, running any of the RxCpp examples fails in lli:

git clone https://github.com/Reactive-Extensions/RxCpp.git --depth 1
cd RxCpp/Rx/v2/examples/pythogerian
clang++ -S -emit-llvm -fno-use-cxa-exit -I../../src main.cpp 
lli main.ll

error-message:

Relocation type not implemented yet!
UNREACHABLE executed at llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp:232!

Questions:

What does this error exactly mean ? - what assumptions are made within llvm's orc-jit that are not satisfied ?

Is there a workaround ? - are there any LLVM-IR transformations i can apply to make this work(e.g. through a compiler-flag) ?

What special features is RxCpp using that cause this problem in llvm's orcjit ?

tested on:

clang version 5.0.0 (https://github.com/llvm-mirror/clang.git 6c9e299494de2a5b0425e46bc937f29a05128252) 
clang version 4.0.0-+rc1-1 (tags/RELEASE_400/rc1)
clang version 3.9.0-1 (tags/RELEASE_390/final)
clang version 3.8.1-12 (tags/RELEASE_381/final)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

Answer 1

Seems to be an issue with thread_local / __thread.

Replacing #define RXCPP_THREAD_LOCAL __thread in rx-utils.hpp with whitespace "fixes" this issue.

The reason is a failure in the LLVM backend as it does not support TLS yet. This is related to Bug 21431 and the fact that some relocation strategies are missing in llvm's RuntimeDyld.