size_t cross-compilation issue

[Alberto Soragna]

Bug report

I'm trying to cross-compile this repository for RaspberryPi (32 bit)

The cross-compilation of this package fails because deserializeSequenceSize function takes a size_t argument and then converts it into `uint64_t.

https://github.com/ros2/rmw_dps/blob/master/rmw_dps_cpp/include/rmw_dps_cpp/CborStream.hpp#L444

error: cannot convert ‘size_t* {aka unsigned int*}’ to ‘uint64_t* {aka long long unsigned int*}’ for argument ‘3’ to ‘DPS_Status CBOR_Peek(DPS_RxBuffer*, uint8_t*, uint64_t*)’
     DPS_Status ret = CBOR_Peek(&buffer_, &maj, size);

Do you think that it is possible to change the GenericCSequence object to directly use the proper type?

https://github.com/ros2/rmw_dps/blob/ab6f8d0257d6cf61fc499fee6ab3936e0b3234f6/rmw_dps_cpp/include/rmw_dps_cpp/macros.hpp

[Todd Malsbary]

The rosidl_generator_c__ functions are defined elsewhere, so it'd probably be more straightforward to have a local uint64_t for the argument, then assign that to the size_t out argument, after some range checking depending on how paranoid you are.

Longer term, it appears that CBOR_Peek is not consistent with other CBOR functions from DPS that take a size_t instead of a uint64_t (i.e. CBOR_DecodeArray). I filed intel/dps-for-iot#96 to track this.

[Todd Malsbary]

Can you provide me some pointers on how to configure ros2 to cross-compile for RaspberryPi? I see a handful of questions and answers online, but I'm not finding anything definitive looking.

[Alberto Soragna]

Yes, you are right.

This is a PR I opened to add RaspberryPi cross-compilation support to the OSRF tools ros-tooling/cross_compile#15

NOTE:

• When cross-compiling the whole ROS2 workspace, it's necessary to find a way to pass the compiler flags to the DPS Sconstruct file. This is an example for a ROS2 vendor package https://github.com/ros2/tinyxml_vendor/blob/master/CMakeLists.txt#L14
  I'm no expert of Scons, so for my tests I simply tried to build the DPS library directly on RaspberryPi

[Alberto Soragna]

@malsbat I tested your new branch https://github.com/intel/dps-for-iot/tree/x86 and it works!

I haven't been able to cross-compile it, but this can be fixed by passing the compilation flags as done in the example I posted above.
However, the changes you did to the source code are enough for building it on 32 bit platforms.

This is what I did in order to test it:

1. On a RaspberryPi ->
   git clone https://github.com/intel/dps-for-iot.git
cd dps-for-iot
git checkout x86
scons variant=release transport=udp bindings=none DEF_FILE=~/rmw_dps/dps_for_iot_cmake_module/librmw_dps_shared.map

2. Copy the ~/dps-for-iot directory to the laptop

3. On the laptop ->
   create a ROS2 workspace
   mkdir -p build/dps_for_iot_cmake_module
mkdir -p install/lib
cp ~/dps-for-iot/build/dist/lib/libdps* install/lib
cp -r ~/dps-for-iot build/dps_for_iot_cmake_module
touch src/rmw_dps/dps_for_iot_cmake_module/COLCON_IGNORE

4. Cross-Compile the ROS2 workspace

[Todd Malsbary]

@alsora Great, I'm going to do a bit more testing with the x86 branch before I merge it. I need to make sure it works on Windows and I'd like to verify your RPi build as well on my end.

[Todd Malsbary]

I did not intend merging PR #9 to close this issue. I want to continue to track the general cross-compilation here.

[Todd Malsbary]

@alsora, I had trouble with the instructions at ros-tooling/cross_compile#15, however I was able to verify PR #33 with the instructions at https://index.ros.org/doc/ros2/Tutorials/Cross-compilation/#cross-compiling-examples-for-arm.

[Todd Malsbary]

I believe this can be closed now with the merge of intel/dps-for-iot#108 and #33.