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Diffstat (limited to 'release_docs/INSTALL_CMake.txt')
| -rw-r--r-- | release_docs/INSTALL_CMake.txt | 81 |
1 files changed, 81 insertions, 0 deletions
diff --git a/release_docs/INSTALL_CMake.txt b/release_docs/INSTALL_CMake.txt index 764feec..c2e2727 100644 --- a/release_docs/INSTALL_CMake.txt +++ b/release_docs/INSTALL_CMake.txt @@ -13,6 +13,7 @@ Section V: Options for building HDF5 Libraries with CMake command line Section VI: CMake option defaults for HDF5 Section VII: User Defined Options for HDF5 Libraries with CMake Section VIII: User Defined Compile Flags for HDF5 Libraries with CMake +Section IX: Considerations for cross-compiling ************************************************************************ @@ -940,6 +941,86 @@ to CMAKE_C_FLAGS. ======================================================================== +IX: Considerations for cross-compiling +======================================================================== + +Cross-compiling has several consequences for CMake: + CMake cannot automatically detect the target platform. + CMake cannot find libraries and headers in the default system directories. + Executables built during cross compiling cannot be executed. + +Cross-compiling support means that CMake separates information about the +build platform and target platform and gives the user mechanisms to solve +cross-compiling issues without additional requirements such as running +virtual machines, etc. + +CMake uses a toolchain of utilities to compile, link libraries and create +archives, and other tasks to drive the build. The toolchain utilities +available are determined by the languages enabled. + +CMake stores info about the current toolchain in the following variables: + CMAKE_C_COMPILER, + CMAKE_CXX_COMPILER. +They contain paths to the C and C++ compilers respectively. This is usually +enough on desktop platforms. In the case of embedded systems, a custom +linker and assembler setting may be needed. In more complex projects +you may need to additionally specify binaries to other parts of the toolchain +(size, ranlib, objcopy…). All these tools should be set in the corresponding +variables: + CMAKE_AR, + CMAKE_ASM_COMPILER, + CMAKE_LINKER, + CMAKE_OBJCOPY, + CMAKE_RANLIB + +As for the host and target operating systems, CMake stores their names in the +following variables: + CMAKE_HOST_SYSTEM_NAME – name of the platform, on which CMake is running (host platform). + On major operating systems this is set to the Linux, Windows or + Darwin (MacOS) value. + CMAKE_SYSTEM_NAME – name of the platform, for which we are building (target platform). + By default, this value is the same as CMAKE_HOST_SYSTEM_NAME, which + means that we are building for the local platform (no cross-compilation). + +Put the toolchain variables into a separate file (e.g. <toolchain_name>.cmake) +and set CMAKE_TOOLCHAIN_FILE variable to the path of that file. +If cmake is invoked with the command line parameter: + --toolchain path/to/file +or + -DCMAKE_TOOLCHAIN_FILE=path/to/file +the file will be loaded early to set values for the compilers. The +CMAKE_CROSSCOMPILING variable is set to true when CMake is cross-compiling. + +Structure of the toolchain file +------------------------------- +In fact, the toolchain file doesn’t have any structure. You can put anything you +want there. But the best practice is to define at least these settings: +path to the toolchain binaries (C compiler, C++ compiler, linker, etc.) +name of the target platform (and optionally target processor architecture) +required compilation and linking flags on that particular platform +toolchain sysroot settings + +It is recommended that you set the CMAKE_FIND_ROOT_PATH variable to a path where +you have an exact copy of the root filesystem you have on your target device (with +libraries and binaries pre-compiled for the target processor). + +References: + https://cmake.org/cmake/help/latest/manual/cmake-toolchains.7.html + https://gitlab.com/embeddedlinux/libs/platform + https://discourse.cmake.org/t/cross-compile-for-aarch64-on-ubuntu/2161/10 + https://stackoverflow.com/questions/54539682/how-to-set-up-cmake-to-cross-compile-with-clang-for-arm-embedded-on-windows?rq=1 + https://developer.android.com/ndk/guides/cmake + +Predefine H5Tinit.c file +------------------------------- +The one file that needs to be pre-generated is the H5Tinit.c file. The variables +indicated in the error log (see above) are the variables that need to match the target system. + +The HDF5 CMake variables; + HDF5_USE_PREGEN: set this to true + HDF5_USE_PREGEN_DIR: set this path to the preset H5Tinit.c file + +======================================================================== For further assistance, send email to help@hdfgroup.org ======================================================================== |