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| = How to use a Linux-to-Linux cross compiling GNU toolchain =
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| Linux is in widespread use in embedded systems and handheld devices. There are many commercial
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| and non-commercial projects which provide cross compiling toolchains, one of these
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| is [http://www.denx.de Denx], which offer the [http://www.denx.de/wiki/DULG/ELDK Embedded Linux Development Kit],
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| short ELDK. ELDK supports PowerPC, ARM and MIPS as target systems, it consists of the cross compiling toolchains and
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| the quite complete target environment.
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| ELDK shouldn't be much different from other cross compiling toolchains, so the information presented here should be usable also for other Linux-to-Linux cross compiling toolchains.
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| == Installing ELDK ==
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| You can find installation instructions at http://www.denx.de/wiki/view/DULG/ELDKDownloadPowerPC , the
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| packages are available at ftp://ftp.sunet.se/pub/Linux/distributions/eldk/ .
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| E.g. if your target has a MIPS processor, you will download the files you can find in
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| ftp://ftp.sunet.se/pub/Linux/distributions/eldk/4.1/mips-linux-x86/iso . The easiest way to use them is to mount
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| these ISO files and then install ELDK using the ''install'' executable you will find there:
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| <pre>
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| ~/ $ mkdir mount-iso/
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| ~/ $ sudo mount -tiso9660 mips-2007-01-21.iso mount-iso/ -o loop
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| ~/ $ cd mount-iso/
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| ~/mount-iso/$ ./install -d /home/alex/eldk-mips/
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| ...
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| Preparing... ########################################### [100%]
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| 1:appWeb-mips_4KCle ########################################### [100%]
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| Done
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| ~/mount-iso/$ ls eldk-mips/
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| bin eldk_init etc mips_4KC mips_4KCle usr var version
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| </pre>
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| In eldk-mips/mips_4KC/ and eldk-mips/mips_4KCle/ the target environments have been installed, i.e. complete Linux
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| filesystems for the target platforms. In eldk-mips/bin/, eldk-mips/usr/ etc. host side tools
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| have been installed, so the cross compiler can be found in eldk-mips/usr/bin/mips-linux-gcc.
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| == Writing a CMake toolchain file ==
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| For CMake to be able to crosscompile software, it requires you to write a toolchain file, which tells CMake
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| some information about the toolchain.
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| With the examples used above it will look like:
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| <pre>
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| # the name of the target operating system
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| SET(CMAKE_SYSTEM_NAME Linux)
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| # which C and C++ compiler to use
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| SET(CMAKE_C_COMPILER /home/alex/eldk-mips/usr/bin/mips_4KC-gcc)
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| SET(CMAKE_CXX_COMPILER /home/alex/eldk-mips/usr/bin/mips_4KC-g++)
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| # here is the target environment located
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| SET(CMAKE_FIND_ROOT_PATH /home/alex/eldk-mips/mips_4KC /home/alex/eldk-mips-extra-install )
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| # adjust the default behaviour of the FIND_XXX() commands:
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| # search headers and libraries in the target environment, search
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| # programs in the host environment
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| set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
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| set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
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| set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
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| </pre>
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| Save this file as Toolchain-eldk-mips4KC.cmake to some location where you will put
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| all your toolchain files, e.g. $HOME.
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| == Building the software for ELDK ==
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| Let's say you have the classical hello world software with a CMake based buildsystem and want to build this for ELDK.
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| main.c:
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| <pre>
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| include <stdio.h>
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| int main()
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| {
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| printf("Hello world\n");
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| return 0;
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| }
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| </pre>
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| CMakeLists.txt:
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| <pre>
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| ADD_EXECUTABLE(hello main.c)
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| INSTALL(TARGETS hello DESTINATION bin)
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| </pre>
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| Then run CMake on it to generate the buildfiles, the important point is that you tell it to use the toochain file you just wrote:
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| <pre>
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| ~/src/helloworld/ $ mkdir build
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| ~/src/helloworld/ $ cd build
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| ~/src/helloworld/build/ $ cmake -DCMAKE_TOOLCHAIN_FILE=~/Toolchain-eldk-mips4KC.cmake -DCMAKE_INSTALL_PREFIX=/home/alex/eldk-mips-extra-install ..
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| -- Configuring done
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| -- Generating done
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| -- Build files have been written to: /home/alex/src/helloworld/build
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| ~/src/helloworld/build/ $ make
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| Scanning dependencies of target hello
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| [100%] Building C object CMakeFiles/hello.dir/main.o
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| Linking C executable hello
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| [100%] Built target hello
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| ~/src/helloworld/build/ $ make install
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| ...
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| -- Installing /home/alex/eldk-mips-extra-install/bin/hello
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| </pre>
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| So that's all. It actually doesn't matter whether it's just a "hello world" or some complex piece of software,
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| the only difference is the usage of the toolchain file. If the software has all required configure checks, it should just
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| build also for ELDK.
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