ld cannot find -lmy_custom_c_library within custom docker image

[lynaghk]

Hi, thanks for Cross --- it's a great tool!

I'm trying to use cross from a Mac to build a binary for Raspberry Pi 0 (arm-unknown-linux-musleabihf).
Plain rust code works great, but I'm having trouble linking to a C library, pigpio.
The error is:

  = note: /usr/local/bin/../lib/gcc/arm-linux-musleabihf/6.4.0/../../../../arm-linux-musleabihf/bin/ld: cannot find -lpigpio

Here's what I've done so far:

1. Built a Docker image that contains my library. I've verified that it exists:

   root@e3c15482d660:/usr/local/lib# file libpigpio.so.1
   libpigpio.so.1: ELF 32-bit LSB shared object, ARM, EABI5 version 1 (SYSV), dynamically linked, stripped
   

2. Specified library search path by adding to build.rs: println!(r"cargo:rustc-link-search=/usr/local/lib");
   I've verified that = note: "arm-linux-musleabihf-gcc" "-Wl,--as-needed" ... [lots of output] contains both "-L" "/usr/local/lib" and "-lpigpio".

I'm running cross via:

cross build --target arm-unknown-linux-musleabihf

and in my Cross.toml have

[target.arm-unknown-linux-musleabihf]
image = "lynaghk/arm-unknown-linux-musleabihf-0.1.16-pigpio"

Within my rust program itself, I'm declaring the C externs:

#[link(name = "pigpio", kind = "dylib")]
extern "C" {
    fn gpioInitialise() -> i32;
}

As far as I understand, this should all work.
I've done it plenty of times when compiling rust natively.
Hopefully I just have a typo somewhere...

Anyway, thanks again for the great tool.
Aside from this linking issue, it's working wonderfully!

[gdesmott]

I'm hitting a similar issue. Did you manage to make it work by any chance? :)

[gdesmott]

Ah, I got it working! Here is how I did:

• cross-built my C library (GStreamer) with prefix=/usr/local
• Installed it to a temp directory (DESTDIR) that I then extracted in the docker image so it's actually installed in /usr/local
• Relied on pkg-config to detect the lib so all the linking paths are automatically configured.

[Alexhuszagh]

As of #727, we've added the search directories for pkg-config to all *-linux-gnu images, however, this won't automatically apply to musl libc images. The solution by @gdesmott is correct, I'll likely add a wiki contribution explaining this in more detail. There's different ways of adding it to the expected search path, but it's pretty important it doesn't interfere with system packages.

[Alexhuszagh]

This has been documented on the wiki and we've added a sample project. If you're building from source, you'll have to make sure it's found by the linker, likely using pkg-config (although other solutions work, like if using CMake). I'll be adding documentation on adding vcpkg binaries as well shortly.

[Alexhuszagh]

FYI: I've fully documented using vcpkg and Conan (along with Meson) on the wiki, including a sample project and automatic integration into Rust.