EcCiA402Drive plugin fails to load at runtime (missing yaml-cpp linkage)

[apajon]

Hi,

I ran into an issue on ROS 2 Jazzy (Ubuntu 24.04) where the EcCiA402Drive plugin fails to load at runtime.

After digging a bit, it turns out both ethercat_generic_slave and ethercat_generic_cia402_drive are built without linking yaml-cpp, which leads to a dlopen failure when pluginlib tries to load the plugin.

I couldn’t find a similar issue reported, so sharing this in case others hit the same problem on Jazzy.

---

Error

[FATAL] [EthercatDriver]: The plugin of platform_to_moving_base failed to load.
Error: Failed to load library .../libethercat_generic_cia402_drive.so.
Error string:
  .../libethercat_generic_slave.so: undefined symbol: _ZTIN4YAML13BadConversionE

Demangled, this is:

typeinfo for YAML::BadConversion

So clearly a missing yaml-cpp symbol at link time.

---

What I checked

ldd libethercat_generic_slave.so | grep yaml
# nothing

ldd libethercat_generic_cia402_drive.so | grep yaml
# nothing

So neither library is linked against yaml-cpp.

---

Root cause (likely)

Both packages rely on:

find_package(yaml_cpp_vendor REQUIRED)
ament_target_dependencies(... yaml_cpp_vendor)

But on Jazzy, yaml_cpp_vendor only sets yaml-cpp_DIR and does not:

• call find_package(yaml-cpp)
• export any targets
• propagate any link libraries

So:

• headers are found → build succeeds
• no actual linkage → runtime crash

---

Fix

Adding an explicit yaml-cpp dependency fixes it.

ethercat_generic_slave

find_package(yaml_cpp_vendor REQUIRED)
find_package(yaml-cpp REQUIRED)

ament_target_dependencies(
  ethercat_generic_slave
  ethercat_interface
  pluginlib
  yaml_cpp_vendor
)

target_link_libraries(
  ethercat_generic_slave
  yaml-cpp::yaml-cpp
)

ethercat_generic_cia402_drive

find_package(yaml_cpp_vendor REQUIRED)
find_package(yaml-cpp REQUIRED)

ament_target_dependencies(
  ethercat_generic_cia402_drive
  ethercat_interface
  ethercat_generic_slave
  pluginlib
  yaml_cpp_vendor
)

target_link_libraries(
  ethercat_generic_cia402_drive
  yaml-cpp::yaml-cpp
)

---

Result

After that:

ldd libethercat_generic_slave.so | grep yaml
→ libyaml-cpp.so

ldd libethercat_generic_cia402_drive.so | grep yaml
→ libyaml-cpp.so

And the plugin loads correctly.

---

Note

This might also be a limitation / bug in yaml_cpp_vendor, but adding the explicit dependency here seems like the safest fix anyway.

Edit: reported by my main account (@apajon)

[apajon]

Hey, reported this from the wrong account earlier.

Just confirming I’m the author — happy to help test or validate a fix if needed.

[fbe555]

Hi.

I have recently made some changes to update the CMakeFiles to use the "modern" package::target syntax, and noticed the yaml_cpp_vendor dependencies where also handled incorrectly. The necessary changes to fix this are included in my pending PR 182.

Can you check if those changes also function as a fix?

[fbe555]

It's been a little while since I made these changes, but as I recall, the correct usage of yaml_cpp_vendor requires something like

    find_package(yaml_cpp_vendor)
    find_package(PkgConfig REQUIRED)
    pkg_check_modules(YAML_CPP REQUIRED yaml-cpp)

And then using the provided cmake variables (YAML_CPP_CFLAGS_OTHER, YAML_CPP_INCLUDE_DIRS, and YAML_CPP_LIBRARIES) as needed in the CMakeList.txt

[apajon]

Hi,
thanks for the pointer!

I can confirm that PR #182 approach works on my setup (ROS 2 Jazzy, Ubuntu 24.04, ros-jazzy-yaml-cpp-vendor 9.0.1, libyaml-cpp-dev 0.8.0).

Root cause confirmed: yaml_cpp_vendor-extras.cmake sets yaml-cpp_DIR but never calls find_package(yaml-cpp), so ament_target_dependencies(... yaml_cpp_vendor) propagates nothing — no targets, no libraries. The .so files compile fine but without -lyaml-cpp, then dlopen fails at runtime on missing YAML symbols.

Tested fix: I applied the pkg_check_modules approach from your PR #182 locally and it resolves the issue — both libethercat_generic_slave.so and libethercat_generic_cia402_drive.so now correctly link libyaml-cpp.so.0.8, and the EcCiA402Drive plugin loads at runtime.

It would be great to see #182 merged — it's been pending for a while and fixes a real blocker on Jazzy.