zstd_vendor breaks CMake when cross-compiling for QNX

[jpsamper2009]

Description

• When cross-compiling rosbag2 for x86_64 QNX, zstd_vendor will download and compile libzstd.so, then copy it to the install directory. libzstd.so is a dependency of the CMake executable on the host, so on the next cmake invocation, the runtime linker finds the QNX version of libzstd.so, causing cmake to fail
• The root cause is that colcon invokes LD_LIBRARY_PATH=/path/to/workspace/install/lib:$LD_LIBRARY_PATH cmake ... in order to make other packages' resources available to the current package; however, this has the side effect of also changing the LD_LIBRARY_PATH for the host's CMake.

Expected Behavior

• Compiling libzstd.so for x86_64 QNX does not interfere with the libzstd.so needed by the cmake on the host.

Actual Behavior

1. zstd is not found for x86_64 QNX
2. zstd_vendor downloads, compiles, and installs libzstd.so in the workspace's install directory
3. cmake is invoked for another package, finding the new libzstd.so
4. Since libzstd.so is compiled for QNX (and not Linux), cmake fails to run

To Reproduce

1. Follow the instructions in https://ros2-qnx-documentation.readthedocs.io/en/galactic/build_from_source.html to compile ROS2 for QNX, except:
   1. In "Building Steps - 5", use CPU=x86_64
   2. Modify build-ros2.sh to invoke colcon twice, the first time with --packages-up-to zstd_vendor, the second time with --packages-select gmock_vendor: i.e.

   build () {
       ...
      colcon build ...
           ...
           --packages-up-to zstd_vendor \
           --cmake-args \
                ....
      colcon build ...
           ...
           --packages-up-to gmock_vendor \
           --cmake-args \
                ....
       ...
   }
   

2. The second colcon command fails with something like:

   /usr/bin/cmake: error while loading shared libraries: libregex.so.1: cannot open shared object file: No such file or directory
   

(Side note: The instructions for compiling ROS2 for QNX are broken in other ways, but it was easier to point to those instructions than to explain here all the other changes that are not related to this bug report)

System

• Host OS/Arch: Linux x86_64
• Target OS/Arch: QNX 7.1 x86_64
• ROS 2 Distro: Galactic, Humble
• Version: See https://ros2-qnx-documentation.readthedocs.io/en/galactic/build_from_source.html

Additional context

• I imagine the fix is to follow a similar scheme to yaml_cpp_vendor where the libraries are installed elsewhere, and the _vendor package makes them available

[jpsamper2009]

Applying the following patch and renaming zstd_vendor-extras.cmake to zstd_vendor-extras.cmake.in seems to fix the issue (but I haven't tested if it breaks other builds).

diff --git a/zstd_vendor/CMakeLists.txt b/zstd_vendor/CMakeLists.txt
index e3d4a22..e682a58 100644
--- a/zstd_vendor/CMakeLists.txt
+++ b/zstd_vendor/CMakeLists.txt
@@ -55,7 +55,7 @@ macro(build_zstd)
 
   install(
     DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}_install/
-    DESTINATION ${CMAKE_INSTALL_PREFIX}
+    DESTINATION ${CMAKE_INSTALL_PREFIX}/opt/zstd_vendor
     USE_SOURCE_PERMISSIONS)
 endmacro()
 
@@ -67,4 +67,4 @@ endif()
 
 install(DIRECTORY cmake DESTINATION share/${PROJECT_NAME})
 
-ament_package(CONFIG_EXTRAS zstd_vendor-extras.cmake)
+ament_package(CONFIG_EXTRAS zstd_vendor-extras.cmake.in)
diff --git a/zstd_vendor/zstd_vendor-extras.cmake b/zstd_vendor/zstd_vendor-extras.cmake
index 07472ac..40287d4 100644
--- a/zstd_vendor/zstd_vendor-extras.cmake
+++ b/zstd_vendor/zstd_vendor-extras.cmake
@@ -1,1 +1,5 @@
+if(NOT DEFINED ENV{zstd_ROOT_DIR})
+  set(zstd_ROOT_DIR "${@PROJECT_NAME@_DIR}/../../../opt/zstd_vendor")
+endif()
+
 list(INSERT CMAKE_MODULE_PATH 0 "${zstd_vendor_DIR}/Modules")

[emersonknapp]

If you propose this change as a pull request, then it would automatically run Ubuntu build and we would run linux-aarch64 and windows build as part of the review process.

"prs welcome" :)

[jpsamper2009]

@emersonknapp For sure. I just wanted to make sure it is the correct approach before going through the effort 😅

[chachoi]

I know this is an old issue, but I found a "fix".

Simply set LD_PRELOAD to libzstd.so's absolute path.

For me it's:
export LD_PRELOAD=$LD_PRELOAD:/usr/lib/x86_64-linux-gnu/libzstd.so.

If you set LD_PRELOAD, your PC would look for the libzstd.so in there first, rather than the libzstd.so which is compiled for QNX.