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| = How to use gcc-multilib to cross compile software for Linux =
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| Goal: compile a 32bits exe on running amd64 linux system.
| | This page has moved [https://gitlab.kitware.com/cmake/community/wikis/doc/cmake/cross_compiling/Gccm32 here]. |
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| == Install the gcc-multilib package ==
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| $ sudo apt-get install gcc-multilib
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| == Write 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 compilers to use for C and C++
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| SET(CMAKE_C_COMPILER gcc)
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| SET(CMAKE_C_FLAGS -m32)
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| SET(CMAKE_CXX_COMPILER g++)
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| SET(CMAKE_CXX_FLAGS -m32)
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| # here is the target environment located
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| SET(CMAKE_FIND_ROOT_PATH /usr/i486-linux-gnu )
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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-gcc-m32.cmake to some location where you will put
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| all your toolchain files, e.g. $HOME.
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| As you can see CMAKE_FIND_ROOT_PATH is set to /usr/i486-linux-gnu, which contains the libraries '''and''' headers
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| installed with the toolchain.
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| == Build the software for Linux ==
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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 Linux
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| using gcc -m32.
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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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| </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 toolchain 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-gcc-m32.cmake -DCMAKE_INSTALL_PREFIX=/home/mathieu/gcc-m32-install ..
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| -- Configuring done
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| -- Generating done
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| -- Build files have been written to: /home/mathieu/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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| </pre>
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| You can then verify:
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| $ file hello
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| hello: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.8, not stripped
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| In case you have a more complex application that is using let say zlib, you would need first to install it:
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| $ apt-cross --arch i386 -i zlib1g-dev
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| And after compilation, you can check that you are indeed using this zlib and not your system one:
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| <pre>
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| $ ldd ./myapp
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| ...
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| libz.so.1 => /usr/i486-linux-gnu/lib/libz.so.1 (0xf7b6b000)
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| ...
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| </pre>
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| {{CMake/Template/Footer}}
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