How to export lib incorporated with C dynllib? - rust

Question

Say, I have a lib package with a C shared library in a sub-directory. This rust library package compiles without errors, by means of tailored build.rs which sub-calls make in the sub-directory and then dynamicly links against the *.so product of make.
The problem arises when I try to link a binary package against this rust lib has the C shared lib within itself.
error: linking with `cc` failed: exit status: 1
= note: /usr/bin/ld: cannot find -lcuda_wrapper
collect2: error: ld returned 1 exit status
The dependency graph can be shown as the following one:
C-shared-lib < rust-lib < rust-bin
And cargo build fails to build rust-bin for not finding that C-shared-lib.
providing LD_LIBRARY_PATH for cargo build neither by command line nor build.rs within rust-bin facilitates the problem and lifts the error.
How to propagate the directory wherein resides libcuda_wrapper.so?

Answer 1

You can link your C library dynamically or statically.
In order to do that you can use add one of the following lines to your build.rs (note that you linkely won't need a lib prefix):
println!("cargo:rustc-link-lib=static=cuda_wrapper");
println!("cargo:rustc-link-lib=dylib=cuda_wrapper");
In order to define a search path, add this line to build.rs
println!("cargo:rustc-link-search=native={}", path);
You would likely want to add it to your rust-lib build.rs. Altenatively, you can create a build.rs for every executable which depends on rust-bin and add the same set of lines here.
It is a good idea to ensure that your C library build output is located under OUT_DIR env variable (you can get it using env::var("OUT_DIR").unwrap() in build.rs). The way cargo clean will work as expected as well.
More details here:
https://doc.rust-lang.org/cargo/reference/build-scripts.html#rustc-link-lib
https://doc.rust-lang.org/rustc/command-line-arguments.html#option-l-link-lib
https://doc.rust-lang.org/cargo/reference/build-script-examples.html#building-a-native-library
https://doc.rust-lang.org/cargo/reference/environment-variables.html