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CMake

Build logic and definitions with CMake language is written either in CMakeLists.txt or a file ends with <project_name>.cmake. But as a best practice, main script is named as CMakeLists.txt instead of .cmake

Indentation is not mandatory but suggested while writing CMake scripts. CMake doesn’t use ‘;’ to understand end of statement.

CMake commands are case insensitive(CMake Variables are case-sensitive). Some commonly used commands,

  • message: prints given message
  • cmake_minimum_required: sets minimum version of cmake to be used
  • add_executable: adds executable target with given name
  • add_library: adds a library target to be build from listed source files
  • add_subdirectory: adds a subdirectory to build

CMake Environment Variables

Some of the environment variables are overriden by predefined CMake Variables. e.g. CXXFLAGS is overriden when CMAKE_CXX_FLAGS is defined.

CMake variables can be set in CMakeLists.txt using set(<variable> <value>, or set through command line cmake -D<var>=<value>

Resources CMake Tutorial

add source files

To add source files in directories, wildcard characters can be use.

file(GLOB_RECURSE sources CONFIGURE_DEPENDS src/*.cpp src/*.hpp include/*.hpp)
add_executable(${PROJECT_NAME} ${sources} )

apply patches

# Look for and apply patches to the third-party (and sub) repo.
file(GLOB PATCHES "${CMAKE_SOURCE_DIR}/patches/*.patch")
if (PATCHES)
  message(STATUS "Patches: ${PATCHES}")
  foreach(PATCH ${PATCHES})
    message(STATUS "Applying ${PATCH}")
    execute_process(
      COMMAND patch -p1 --forward --ignore-whitespace
      WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}"
      INPUT_FILE "${PATCH}"
      OUTPUT_VARIABLE OUTPUT
      RESULT_VARIABLE RESULT)
    if (RESULT EQUAL 0)
      message(STATUS "Patch applied: ${PATCH}")
    else()
      # Unfortunately although patch will recognise that a patch is already
      # applied it will still return an error.
      execute_process(
        COMMAND patch -p1 -R --dry-run
        WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}"
        INPUT_FILE "${PATCH}"
        OUTPUT_VARIABLE OUTPUT
        RESULT_VARIABLE RESULT2)
      if (RESULT2 EQUAL 0)
        message(STATUS "Patch was already applied: ${PATCH}")
      else()
        message(FATAL_ERROR "Error applying patch ${PATCH}")
      endif()
    endif()
  endforeach(PATCH)
endif()

source

Raspberry Pi cross compilation

  • GCC/G++ dynamic linking with pthread error
arm-linux-gnueabihf/libpthread.a(pthread_create.o): In function __pthread_create_2_1
pthread_create.c:697: undefined reference to _dl_stack_flags
libpthread.a(unwind.o): In function 'unwind_stop':
...

Because libpthread.so is not found, libpthread.a is picked. Solution: Check the symlink for libpthread.so in the sysroot under /usr/lib/arm-linux-gnueabihf credit

#!/bin/bash

export CROSS_COMPILE=${CROSS_COMPILE:-arm-linux-gnueabihf-}

check_toolchain () {
  if ! ( which ${CROSS_COMPILE}gcc \
      && which ${CROSS_COMPILE}as  \
      && which ${CROSS_COMPILE}ld ) ; then
      echo "Could not find cross toolchain"
      exit 1
  fi
}

check_toolchain

export sysroot=[ROOTFS FOLDER]

mkdir arm32hf_build
cd arm32hf_build

cmake ../ \
-DCMAKE_SYSTEM_NAME=Linux \
-DCMAKE_SYSTEM_PROCESSOR=armv7l \
-DCMAKE_SYSROOT=${sysroot} \
-DCMAKE_FIND_ROOT_PATH=${sysroot} \
-DCMAKE_C_COMPILER=${CROSS_COMPILE}gcc \
-DCMAKE_CXX_COMPILER=${CROSS_COMPILE}g++ \
-DCMAKE_CXX_FLAGS="-Wl,-rpath-link=${sysroot}/usr/lib/arm-linux-gnueabihf" \
-DCMAKE_FIND_ROOT_PATH_MODE_PROGRAM=NEVER \
-DCMAKE_FIND_ROOT_PATH_MODE_LIBRARY=ONLY \
-DCMAKE_FIND_ROOT_PATH_MODE_INCLUDE=ONLY \
-DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=ONLY \
-DCMAKE_POSITION_INDEPENDENT_CODE=True \
-DCMAKE_EXE_LINKER_FLAGS="--sysroot=${sysroot} -Wl,-rpath-link=${sysroot}/lib/arm-linux-gnueabihf" \
-DCMAKE_SHARED_LINKER_FLAGS="--sysroot=${sysroot}" \
-DCMAKE_BUILD_TYPE=Release \
-DCMAKE_INSTALL_PREFIX=./install

cmake --build .
make install