Rust and loader paths (#rpath, #loader_path) on OS X - macos

Question

I'm trying to solve a problem with foreign library loading with Rust.
Inputs:
I have an executable rtest and a dylib libcpp2rs.dylib. The library is linked to the executable through FFI:
#[link(name="cpp2rs")]
extern { ... }
My build.rs file (I'm passing an extra argument with libcpp2rs.dylib location):
pub fn main() {
println!("cargo:rustc-link-search=native=./cpplib/bin");
}
And my Cargo.toml file:
[package]
name = "rtest"
version = "0.1.0"
authors = ["astavonin"]
build = "build.rs"
rpath = true
[dependencies]
libc = "0.2.10"
And I use cargo build command for compilation.
Outputs:
otool shows me that library will be loaded by RPATH:
> otool -L rtest
rtest:
#rpath/libcpp2rs.dylib (compatibility version 0.0.0, current version 0.0.0)
/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1226.10.1)
But at the same time there is no LC_LPATH section in executable:
> otool -l rtest | grep LC_RPATH
>
And it leads my application to a loading error:
> ./rtest
dyld: Library not loaded: #rpath/libcpp2rs.dylib
Referenced from: /Users/astavonin/projects/Tests/rtest/target/debug/./rtest
Reason: image not found
zsh: trace trap ./rtest
This issue can be fixed by install_name_tool usage, but I prefer do not introduce additional steps into compilation process.
Is it possible (and how) to change loading type from #rpath to #loader_path with cargo configurations/build script?
Is it possible to pass #rpath value to cargo?

Answer 1

After some researches around I've found that the actual problem is libcpp2rs.dylib ID:
> otool -L cpplib/bin/libcpp2rs.dylib
cpplib/bin/libcpp2rs.dylib:
#rpath/libcpp2rs.dylib (compatibility version 0.0.0, current version 0.0.0)
/usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 120.1.0)
/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1226.10.1)
rustc uses a dylib ID as a reference for linkage type and if you'd like to change linkage type for a library to #loader_path for example, you have to fix dylib ID. It should looks like:
#loader_path/libcpp2rs.dylib (compatibility version 0.0.0, current version 0.0.0)