rust_main undefined on latest nightly

[iakshay]

I'm using linux kernel 4.20.6 and the following clang and rust versions[0]. The make command succeds for me, but I get the following warning. Seems like the module compiles successfully but the linking to rust library is broken.

WARNING: "rust_main" [/usr/src/rust.ko/build/hello.ko] undefined!

Let me know if more information is needed to debug this issue.
[0]:

[root@host rust.ko]# rustc --version
rustc 1.35.0-nightly (70f130954 2019-04-16) 
[root@host rust.ko]# clang --version
clang version 5.0.1 (tags/RELEASE_501/final) 
Target: x86_64-unknown-linux-gnu 
Thread model: posix  
InstalledDir: /opt/rh/llvm-toolset-7/root/usr/bin