"undefined reference to `<function>()'"

[voltangle]

Hi guys! I love that someone actually made something like this, because it removes a lot of problems when integrating Rust in a C/C++ CMake project. Although I managed to make a lot of stuff work, I have a problem, and you have probably already guessed what is it. Linker doesn't find functions in a compiled Rust crate, and I have no idea who and what actually shat the bed and in what direction do I need to look at to fix this issue.

I can't make a reproducible example, so here is the whole project(sorry): https://github.com/ggoraa/edgetx/tree/eldb

But I will also show some relevant files here:
radio/src/rs/src/lib.rs:

#![no_std]
use core::panic::PanicInfo;

mod bindings;

#[panic_handler]
fn halt(info: &PanicInfo) -> ! {
    loop { }
}

#[no_mangle]
pub unsafe extern "C" fn this_function_exists_in_c() -> u32 {
    bindings::cliGetMode()
}

radio/src/rs/CMakeLists.txt:

include(FetchContent)

set(Rust_CARGO_TARGET "thumbv7em-none-eabihf")

FetchContent_Declare(
    Corrosion
    GIT_REPOSITORY https://github.com/corrosion-rs/corrosion.git
    GIT_TAG v0.3.5 # Optionally specify a commit hash, version tag or branch here
)
FetchContent_MakeAvailable(Corrosion)

corrosion_import_crate(MANIFEST_PATH ${RADIO_SRC_DIR}/rs/Cargo.toml NO_STD)
corrosion_set_linker(rs "ld")

include_directories(${RADIO_SRC_DIR}/rs/pub_headers)

target_link_options(firmware PUBLIC "-Wl,--allow-multiple-definition")
target_link_options(firmware PUBLIC "-static")
target_link_libraries(firmware PUBLIC rs)

radio/src/rs/Cargo.toml:

[package]
name = "etx-rs"
version = "2.9.0"
edition = "2021"

[lib]
name = "rs"
crate-type = ["staticlib"]
test = false
bench = false

[build-dependencies]
cbindgen = "0.20.0"
bindgen = "0.53.1"

[dependencies]
cty = "0.2"

Error itself:

<file>: undefined reference to `this_function_exists_in_c()'
collect2: error: ld returned 1 exit status

All relevant files are in radio/src directory.

To compile, use this command: cd build && cmake -DPCB=X7 -DCLI=1 -DGCC_ARM_PATH=/Applications/ARM/bin/ -DPYTHON_EXECUTABLE=/usr/local/bin/python3 .. inside a build dir, as usual.

Btw, this project is compiled for STM32, basically ARM Cortex-M

Can you guys help me resolve this issue?

[jschwe]

Could you post the complete command you use to configure and build the project in the devcontainer of the project?
Is the error message you received the complete error message?

[voltangle]

(I am on macOS btw, here is how to do it for other platforms: https://github.com/EdgeTX/edgetx/wiki/Building-and-debugging-EdgeTX)

[jschwe]

I can't build the project in the provided devcontainer, due to missing dependencies.

CMake Error at radio/src/lua/debugger/CMakeLists.txt:2 (find_package):
  By not providing "FindNanopb.cmake" in CMAKE_MODULE_PATH this project has
  asked CMake to find a package configuration file provided by "Nanopb", but
  CMake did not find one.

  Could not find a package configuration file provided by "Nanopb" with any
  of the following names:

    NanopbConfig.cmake
    nanopb-config.cmake

Could you provide a log where you run the build with cmake --verbose (with make it would be make VERBOSE=1)? This should print the command line the linker was invoked with.

Some comments about your CMakeLists.txt

corrosion_set_linker(rs "ld")

This line is useless for staticlibs, since Rust does not invoke the linker for them (on master corrosion issues a warning in such cases). You can just remove it.

target_link_options(firmware PUBLIC "-Wl,--allow-multiple-definition")

Why do you need this option? You really should not pass this flag unless you have a really good reason and know what you are doing! What are the errors you are seeing when you remove this flag?

target_link_options(firmware PUBLIC "-static")

Are you sure you need this flag?

[voltangle]

First and last flags are here just because I was trying any option I could find to try to make it work. The second flag though is because I was getting errors on multiple definitions, that flag fixed it

I can't build the project in the provided devcontainer, due to missing dependencies.

You have probably checked out without submodules, because Nanopb is added using a submodule

[jschwe]

You have probably checked out without submodules, because Nanopb is added using a submodule

Thanks, initializing the submodules helped.

I got a little further, but still am not at the point you are.

Issue 1: bindgen fails due to libclang not finding stdint.h. In response I added .clang_arg("-I/opt/gcc-arm-none-eabi-10-2020-q4-major/arm-none-eabi/include"), which helps, but afterwards stddef.h is not found (used in cli.h). stddef.h` doesn't seem to be provided by the gcc toolchain in the docker image.

issue 2: commenting the stddef.h include got me further, and the rust library was built successfully. New error:

[ 34%] Generating nanopb/generator/proto/nanopb_pb2.py
Traceback (most recent call last):
  File "/workspaces/edgetx/radio/src/thirdparty/nanopb/generator/protoc", line 44, in <module>
    status = invoke_protoc(['protoc'] + args)
  File "/workspaces/edgetx/radio/src/thirdparty/nanopb/generator/proto/_utils.py", line 44, in invoke_protoc
    return subprocess.call(argv)
  File "/usr/lib/python3.6/subprocess.py", line 287, in call
    with Popen(*popenargs, **kwargs) as p:
  File "/usr/lib/python3.6/subprocess.py", line 729, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.6/subprocess.py", line 1364, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'protoc': 'protoc'
radio/src/CMakeFiles/firmware.dir/build.make:81: recipe for target 'radio/src/nanopb/generator/proto/nanopb_pb2.py' failed

[voltangle]

I am really sorry for making you spin up a whole environment for building this :(
It wants a protobuf compiler, protoc
It should be just installed using a package manager

Dev containers will also be improved later and work as expected, with all dependencies included

[jschwe]

I can reproduce your issue now, but I'm not sure why your linker doesn't see the symbol.

Regarding the multiple definitions issue - this is an upstream rust issue (rust-lang/rust#104707). In the issue, this blog post was linked and describes a way to work around this issue.