Feature/toolchain cmake cross

[memsharded]

Changelog: Feature: Initial cross-build support in CMakeToolchain with definition of CMAKE_SYSTEM_NAME, CMAKE_SYSTEM_PROCESSOR and CMAKE_SYSTEM_VERSION, deduced from self.settings_build (only using the 2 profiles) and from new [conf] items.
Docs: conan-io/docs#2140

Close #9072

[lasote]

Looking good!

• Missing docs
• I'm wondering if we should add moreconf entries for the rest of the typical stuff that CMake uses in a toolchain file. How would be the alternative for the user without modifying the recipe ( toolchain blocks ) ?

set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_PROCESSOR arm)

set(CMAKE_SYSROOT /home/devel/rasp-pi-rootfs)
set(CMAKE_STAGING_PREFIX /home/devel/stage)

set(tools /home/devel/gcc-4.7-linaro-rpi-gnueabihf)
set(CMAKE_C_COMPILER ${tools}/bin/arm-linux-gnueabihf-gcc)
set(CMAKE_CXX_COMPILER ${tools}/bin/arm-linux-gnueabihf-g++)

set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)

[memsharded]

I'm wondering if we should add moreconf entries for the rest of the typical stuff that CMake uses in a toolchain file. How would be the alternative for the user without modifying the recipe ( toolchain blocks ) ?

It is possible to directly inject a complete toolchain, with "tools.cmake.cmaketoolchain:user_toolchain" conf, in the UserToolchain block. Is this what you want?

Regarding the CMAKE_FIND_ROOT_PATH_MODE_LIBRARY variables, yes, maybe we should add some of those lines directly in the toolchain?

[KerstinKeller]

I just saw this PR, and I wanted to give some feedback. We're currently using some dirty hacks to induce the correct Toolchain files for cross builds.
Basically every profile which is a cross compilation profile, sets an environment variable

[env]
TOOLCHAIN_FILE=/common/toolchain-files/arm64_toolchainfile.cmake

But this toolchain file is usually present in the docker images which run the build, back then we didn't find a better solution.

Also it's nice that Conan will now offer to generate these toolchains (or induce variables in the generic toolchain), however from my experience, (real life) cmake toolchain files for cross compilation go beyond just setting sysroot and the compilers, so it might be hard for Conan to generate them correctly.

If profiles could reference existing CMake toolchain files (e.g. don't know where they could be stored, ideally with/next to the profile), and if these existing toolchains would be induced to the one that Conan generates, or (if the user doesn't use the toolchain generator, if Conan could provide a path to the specified toolchain in the profile), that would be extremly useful and beneficial.

[memsharded]

Hi @KerstinKeller

If I understood correctly, I think that this is already available in 1.37 in the [conf] of your profile:

• tools.cmake.cmaketoolchain:user_toolchain in your profile will include(xxx) that information from the conan_toolchain.cmake
• tools.cmake.cmaketoolchain:toolchain_file will completely replace the conan_toolchain.cmake by the user provided one.

Does this help? Is this the feature that you want?
Maybe one UX issue is the definition of paths, that would be absolute or something, something we need to check.

[KerstinKeller]

@memsharded
Ah perfect 👍 , I seem never to be able to keep up with all the new features available 🙈

about the paths of the toolchain files, they are usually tightly coupled to proflex, e.g. one toolchain file per profile, so it would be cool to have it there. Alternative could be a build_requires package, that contains the toolchain, but then I have no clue how to reference that from the profile...

[memsharded]

Alternative could be a build_requires package, that contains the toolchain, but then I have no clue how to reference that from the profile...

We also introduced the possibility for build_requires to pass [conf] items to their consumers, so if the toolchain is inside a package that is build_required it could define that config and point it to its own file: https://docs.conan.io/en/latest/reference/config_files/global_conf.html#configuration-from-build-requires

[KerstinKeller]

Oh that's very good to know and very handy! Thanks for the info!

[memsharded]

Oh that's very good to know and very handy! Thanks for the info!

:)

Keep in mind that it is experimental, we are doing a ton of work in this, and this is expected to evolve. Feedback very welcome of course!

[lasote]

Don't forget the docs and explain that tools.cmake.cmaketoolchain:user_toolchain invalidates the cross build block