Need help to add ament_index_register_resource in px4_msgs CMakeLists.txt

[agwegsol]

I am trying to use the latest px4-ros2-interface-lib but is having a problem with the build system.

Note, I am not using colcon, since I compile is a virtual plus cross compile environment. Colcon gets confused since it assumes "stuff" and start using the native objects during compile. This is a no go, so I am using pure CMake.

But I can not build latest px4-ros2-interface-lib do to this line in the CMakefile.txt
ament_index_get_resource(MESSAGE_FILES "rosidl_interfaces" px4_msgs)

From what I can read in the CMakeLists.txt file, the line is used to generate a header file containing all px4_msgs header files. The list is fetched from the px4_msgs CMake cache using ament_index_get_resource. But the resource is not there and thus needs to be added.
If I compile using SHA=396120292cc70014c37646d30fccc2c62a649458, just before the commit adding the header file all compile just fine so my setup is working (sort of)

I am using ros2 kilted in both native in cross compile environment, all in a virtual env.

I compile the px4_msgs using this CMakeLists.txt, from https://github.com/PX4/px4_msgs

cmake_minimum_required(VERSION 3.5)

project(px4_msgs)

list(INSERT CMAKE_MODULE_PATH 0 "${CMAKE_CURRENT_SOURCE_DIR}/cmake")

if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
	add_compile_options(-Wall -Wextra)
endif()

find_package(ament_cmake REQUIRED)
find_package(builtin_interfaces REQUIRED)
find_package(rosidl_default_generators REQUIRED)

# ##############################################################################
# Generate ROS messages, ROS2 interfaces and IDL files #
# ##############################################################################

# get all msg files
set(MSGS_DIR "${CMAKE_CURRENT_SOURCE_DIR}/msg")
file(GLOB PX4_MSGS RELATIVE "${CMAKE_CURRENT_SOURCE_DIR}" "${MSGS_DIR}/*.msg")

# get all srv files
set(SRVS_DIR "${CMAKE_CURRENT_SOURCE_DIR}/srv")
file(GLOB PX4_SRVS RELATIVE "${CMAKE_CURRENT_SOURCE_DIR}" "${SRVS_DIR}/*.srv")

# Generate introspection typesupport for C and C++ and IDL files
rosidl_generate_interfaces(${PROJECT_NAME}
	${PX4_MSGS}
	${PX4_SRVS}
	DEPENDENCIES builtin_interfaces
)

ament_export_dependencies(rosidl_default_runtime)

ament_package()

But there is no ament_index_register_resource and I think this is the problem
I have read the Ament-CMake-Documentation, did some trail and error but did not manage to make it work. So, does someone know how to add the resource?

A hint will be most appreciated.

[bkueng]

I'm not sure how ament handles the index, so I can't help directly.
What we could do is adding a cmake option to disable this part - it's used for message compatibility check and only when using zenoh as middleware.

We also struggled with ros cross-compilation.
In case it helps, we ended up building a cross-compilation container like this:

# Setup cross compile toolchain
RUN apt update && \
    apt install -y \
        crossbuild-essential-arm64 \
        crossbuild-essential-amd64 \
        gcc-aarch64-linux-gnu g++-aarch64-linux-gnu binutils-aarch64-linux-gnu \
        gcc-x86-64-linux-gnu g++-x86-64-linux-gnu binutils-x86-64-linux-gnu

RUN echo "\
set(CMAKE_SYSTEM_NAME Linux)\n\
set(CMAKE_SYSTEM_PROCESSOR aarch64)\n\
set(CMAKE_C_COMPILER aarch64-linux-gnu-gcc)\n\
set(CMAKE_CXX_COMPILER aarch64-linux-gnu-g++)\n\
set(CMAKE_FIND_ROOT_PATH /opt/sysroot)\n\
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)\n\
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)\n\
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)\n\
set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)\n\
set(CMAKE_SYSROOT /opt/sysroot)\n\
set(AMENT_PREFIX_PATH /opt/sysroot/opt/ros/humble)\n\
set(PYTHON_SOABI cpython-310-aarch64-linux-gnu)\n\
" > /Toolchain_arm64.cmake

RUN echo "\
set(CMAKE_SYSTEM_NAME Linux)\n\
set(CMAKE_SYSTEM_PROCESSOR x86_64)\n\
set(CMAKE_C_COMPILER x86_64-linux-gnu-gcc)\n\
set(CMAKE_CXX_COMPILER x86_64-linux-gnu-g++)\n\
set(CMAKE_FIND_ROOT_PATH /opt/sysroot)\n\
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)\n\
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)\n\
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)\n\
set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)\n\
set(CMAKE_SYSROOT /opt/sysroot)\n\
set(AMENT_PREFIX_PATH /opt/sysroot/opt/ros/humble)\n\
set(PYTHON_SOABI cpython-310-x86_64-linux-gnu)\n\
" > /Toolchain_amd64.cmake

# Hack: ROS IDL seems to be looking in the wrong place for this library when cross compiling
RUN ln -snf /opt/sysroot/usr/lib/aarch64-linux-gnu/libpython3.10.so /usr/lib/aarch64-linux-gnu/libpython3.10.so
RUN ln -snf /opt/sysroot/usr/lib/x86_64-linux-gnu/libpython3.10.so /usr/lib/x86_64-linux-gnu/libpython3.10.so

And then building a workspace in docker like this:

# 1. -- Sysroot build stage. Runs in target arch emulation (QEMU) --
# Install ROS & dependencies
FROM ubuntu:latest as sysroot-stage

# RUN apt update && apt install -y \
    [...] && \
    apt clean && \
    rm -rf /var/lib/apt/lists/*

# 2. -- Cross-compile build stage. Runs on host arch (NATIVE) --
FROM --platform=$BUILDPLATFORM app-cross-env:v2 as build-stage

# Declare automatically defined global scope Docker arg
# The variable TARGETARCH is defined by the buildx build process and contains either "arm64" or "amd64"
ARG TARGETARCH

# Copy sysroot from sysroot-stage
# We will then use this sysroot to link against in the cross-compilation
COPY --from=sysroot-stage / /opt/sysroot

# Compile the source using the appropriate Toolchain file
WORKDIR /opt/sysroot/app
COPY src /opt/sysroot/app/src
RUN . ./install/setup.sh && \
    colcon build --cmake-args -DCMAKE_TOOLCHAIN_FILE=/Toolchain_$TARGETARCH.cmake

# 3. -- Runtime stage. Runs in target architecture emulation and on target --
FROM sysroot-stage as run-stage

COPY --from=build-stage /opt/sysroot/app/install /opt/sysroot/app/install
COPY --from=build-stage /opt/sysroot/app/build /opt/sysroot/app/build
CMD . /opt/sysroot/opt/ros/humble/install/setup.sh && \
    . /opt/sysroot/app/install/local_setup.sh && \
    /opt/sysroot/app/build/my_package/binary

You will need to adjust it to your needs though (ros version, etc).

[agwegsol]

Thanks for the answer. A least now I know I am not the only one having problems with ros2+cross compile.
I will search for a solution and post the solution (if any)

[agwegsol]

I looked a bit deeper and this ament_cmake+colcon is not ready for a cross compiler in a virtual setup. It is possible to use pure CMake but the px4-ros2-interface-lib, needs some changes to make this possible. That is, get rid of colcon and limit the use off ament cmake.
I have not looked deep into this, but it seems that ament_cmake also "assumes stuff" which breakes a cross compiler. One example, when sourcing //setup.sh the LD_LIBRARY_PATH is set. That is a very bad idea and will brake most Cross builds, is should be handled by the CMake.
For this reason I will skip the library, get inspired but that is it.