Using host tools for cross compilation

Say you have to generate sources during the build. You do so using an executable called footool.

In the tutorial we assume you have two configs:

• linux64, associated to a toolchain containing for instance pre-compiled dependencies of footool
• arm, associated to a cross-toolchain targeting arm

The code looks like this:

worktree
  footool
    qiproject.xml
    CMakeLists.txt
    foo-config.cmake
    footool.cpp

// In footool.cpp

int main(int argc, char* argv)
{
  char* input = argv[1];
  char* output = argv[2];

  // Generate output from input

}

# in CMakeLists.txt

qi_create_bin(footool footool.cpp)
qi_stage_bin(footool)

qi_stage_cmake(foo-config.cmake)



# in foo-config.cmake

find_package(footool REQUIRED)

function(generate_foo output input)

  qi_generate_src(${output}
    COMMAND ${FOOTOOL_EXECUTABLE} ${input} ${output}
  )

endfunction()

You then have an other project which uses footool to generate some sources:

worktree
  footool
  usefootool
    qiproject.xml
    CMakeLists.txt

# In CMakeLists.txt

find_package(foo REQUIRED)

generate_foo(out src.cpp)

# ...

So what you need is to configure and build the footool project so the binary footool exists, and find the footool executable in the build directory of the footool project even when you are for instance cross-compiling.

To do so, you should:

• Patch the qiproject.xml to add a host dependency to footool

<!-- in usefootool/qiproject.xml -->
<project version="3">
  <qibuild name="usefootool">
    <depends host="true" names="footool" />
  </qibuild>
</project>

• Tell qibuild to use a host config.

  qibuild set-host-config linux64
  

• Configure and build the footool project:

  qibuild configure footool -c linux64
  qibuild make footool -c linux64
  

• Then you can cross-compile for arm:

  qibuild configure usefootool -c arm
  qibuild make usefootool -c arm
  

If you are not using any toolchain, you can of course just configure and build usefootool normally:

qibuild configure footool
qibuild make footool

qibuild configure usefootool -c arm
qibuild make usefootool -c arm

• Alternatively, you can use qibuild make-host-tools from the usefootool directory. It will parse the host dependencies of the current build project and build them.

  cd usefootool
  qibuild make-host-tools