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CMake: Toolchain File

When we have a build system like Yocto or Buildroot, cross compiling a CMake project is a simple task - We just need to create a simple CMake inherited recipe. If the SoC vendor only provides toolchain for you to cross compile a single CMake project, CMake toolchain file is a good approach.

What is CMake Toolchain File

CMake has a variable CMAKE_TOOLCHAIN_FILE:

This variable is specified on the command line when cross-compiling with CMake. It is the path to a file which is read early in the CMake run and which specifies locations for compilers and toolchain utilities, and other target platform and compiler related information.

Toolchain File Example

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SET(CMAKE_SYSTEM_NAME Linux)
# specify the cross compiler
SET(CMAKE_C_COMPILER /toolchain/gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-gcc)
SET(CMAKE_CXX_COMPILER /toolchain/gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-g++)

SET(CMAKE_FIND_ROOT_PATH /toolchain/gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu/)

SET(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
SET(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
SET(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
  • CMAKE_FIND_ROOT_PATH: This variable tells CMake find_* commands need to look into this sysroot.
  • CMAKE_FIND_ROOT_PATH_MODE_LIBRARY: This variable controls whether the CMAKE_FIND_ROOT_PATH and CMAKE_SYSROOT are used by find_library(). We set to ONLY, so CMake will find_library under this path only.
  • CMAKE_FIND_ROOT_PATH_MODE_INCLUDE: This variable controls whether the CMAKE_FIND_ROOT_PATH and CMAKE_SYSROOT are used by find_file() and find_path(). We set to ONLY, so CMake will look into this path only.