A cross compiler is a compiler capable of creating executable code for a platform other than the one on which the compiler is running. For example, a compiler that runs on a Windows 7 PC but generates code that runs on Android smartphone is a cross compiler.
Before we continue, there issome definitions we need to decide.
--host option).--host option).--target option).Note: To decide the values of the above configuration, simply run gdb --version on the native machine. for a linux machine it's x86_64-pc-linux-gnu and for my target machine it's amd64-marcel-freebsd9.2. Since we're building and running our cross-compile on the same machine (x86_64-pc-linux-gnu), we don't need to specify the build and the host configuration which gcc will pick automatically.
$ export TARGET=amd64-marcel-freebsd9.2
And since, we don't wan to mix our cross-compile toolchains with our native binaries, we install our cross-compiler toolchains in the /usr/cross-build directory:
$ export PREFIX=/usr/cross-build
$ export TARGET_PREFIX=$PREFIX/$TARGET
$ export PATH=$PATH:$PREFIX/bin
One more important note before start compiling is that we need the head-files and libraries of the target machine. So we should copy /lib and /include directories from our freebsd machine to our cross-build directory:
$ mkdir -p $TARGET_PREFIX{,/lib,/include}
# copy /lib and /include directories from our freebsd machine in our target $TARGET_PREFIX directory.
GCC requires that a compiled copy of binutils be available for each targeted platform. So we need to download the source code of binutils and compile it for the freebsd machine.
$ mkdir -p build-binutils
$ wget https://ftp.gnu.org/gnu/binutils/binutils-2.27.tar.gz
$ tar zxvf binutils-2.27.tar.gz
$ cd build-binutils
$ ../binutils-2.27/configure --target=$TARGET --prefix=$PREFIX -v
$ make -j 4
$ sudo make install
GCC also depends on the following components: * GMP: GNU Multiple Precision Arithmetic Library * MPFR: GNU Multiple-precision floating-point rounding library * MPC: GNU Multiple-precision C library
To build our cross-compiler, we need to compile these dependencies but since these dependencies should produce code for our target machine, we need to build them for the host option set to our tagret (--host=amd64-marcel-freebsd9.2):
$ mkdir build-gmp
$ wget https://ftp.gnu.org/gnu/gmp/gmp-6.1.1.tar.xz
$ tar xvf gmp-6.1.1.tar.xz
$ cd build-gmp
$ ../gmp-6.1.1/configure --prefix=$PREFIX --enable-shared --enable-static --enable-mpbsd --enable-fft --enable-cxx --host=$TARGET
$ make -j 4
$ sudo make install
$ cd ..
$ mkdir build-mpfr
$ wget https://ftp.gnu.org/gnu/mpfr/mpfr-3.1.5.tar.xz
$ tar xvf mpfr-3.1.5.tar.xz
$ cd build-mpfr
$ ../mpfr-3.1.5/configure --prefix=$PREFIX --with-gnu-ld --with-gmp=$PREFIX --enable-static --enable-shared --host=$TARGET
$ make -j 4
$ sudo make install
$ cd ..
$ mkdir build-mpci
$ wget https://ftp.gnu.org/gnu/mpc/mpc-1.0.3.tar.gz
$ tar zxvf mpc-1.0.3.tar.gz
$ cd build-mpc
$ ../mpc-1.0.3/configure --prefix=$PREFIX --with-gnu-ld --with-gmp=$PREFIX --with-mpfr=$PREFIX --enable-static --enable-shared --host=$TARGET
$ make -j 4
$ sudo make install
$ cd ..
Finally, to compile gcc we need to specify where to look for it's dependencies above:
$ mkdir build-gcc
$ wget https://ftp.gnu.org/gnu/gcc/gcc-6.2.0/gcc-6.2.0.tar.gz
$ tar zxvf gcc-6.2.0.tar.gz
$ cd build-gcc
$ ../gcc-6.2.0/configure --without-headers --with-gnu-as --with-gnu-ld --enable-languages=c,c++ --disable-nls --enable-libssp --enable-gold --enable-ld --target=$TARGET --prefix=$PREFIX --with-gmp=$PREFIX --with-mpc=$PREFIX --with-mpfr=$PREFIX --disable-libgomp
$ LD_LIBRARY_PATH=$PREFIX/lib make -j 4
$ sudo make install
Now, we should have our own cross-compiler's toolchain in /usr/cross-build/bin directory. To use it we should include it in our $PATH:
export PATH=$PATH:$PREFIX/bin
To test our own cross-compiler, we simply run:
$ gcc main.c -o helloworld-linux
$ file helloword-linux
main: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=ca5ba57ac722ef8521d50ee8ecbbdca4b44a76e1, not stripped
$ LD_LIBRARY_PATH=$PREFIX/lib amd64-marcel-freebsd9.2-gcc helloworld.c -o helloworld-freebsd
$ file helloworld-freebsd
main: ELF 64-bit LSB executable, x86-64, version 1 (FreeBSD), dynamically linked, interpreter /libexec/ld-elf.so.1, for FreeBSD 9.2, not stripped
If you need a cross-compile version of gdb, simply compile the gdb for the target machine like above:
$ wget https://ftp.gnu.org/gnu/gdb/gdb-7.11.tar.xz
$ tar xvf gdb-7.11.tar.xz
$ ../gdb-7.11.1/configure --prefix=$PREFIX --target=$TARGET
$ make -j 4
$ sudo make install
You can see the whole compile process in my github gist.