2.2.8 Cross-Compilation

To cross-compile is to build on one platform a binary that will run on another platform. When speaking of cross-compilation, it is important to distinguish between the build platform on which the compilation is performed, and the host platform on which the resulting executable is expected to run. The following configure options are used to specify each of them:

--build=build

The system on which the package is built.

--host=host

The system where built programs and libraries will run.

When the --host is used, configure will search for the cross-compiling suite for this platform. Cross-compilation tools commonly have their target architecture as prefix of their name. For instance my cross-compiler for MinGW32 has its binaries called i586-mingw32msvc-gcc, i586-mingw32msvc-ld, i586-mingw32msvc-as, etc.

Here is how we could build amhello-1.0 for i586-mingw32msvc on a GNU/Linux PC.

     ~/amhello-1.0 % ./configure --build i686-pc-linux-gnu --host i586-mingw32msvc
     checking for a BSD-compatible install... /usr/bin/install -c
     checking whether build environment is sane... yes
     checking for gawk... gawk
     checking whether make sets $(MAKE)... yes
     checking for i586-mingw32msvc-strip... i586-mingw32msvc-strip
     checking for i586-mingw32msvc-gcc... i586-mingw32msvc-gcc
     checking for C compiler default output file name... a.exe
     checking whether the C compiler works... yes
     checking whether we are cross compiling... yes
     checking for suffix of executables... .exe
     checking for suffix of object files... o
     checking whether we are using the GNU C compiler... yes
     checking whether i586-mingw32msvc-gcc accepts -g... yes
     checking for i586-mingw32msvc-gcc option to accept ANSI C...
     ...
     ~/amhello-1.0 % make
     ...
     ~/amhello-1.0 % cd src; file hello.exe
     hello.exe: MS Windows PE 32-bit Intel 80386 console executable not relocatable

The --host and --build options are usually all we need for cross-compiling. The only exception is if the package being built is itself a cross-compiler: we need a third option to specify its target architecture.

--target=target

When building compiler tools: the system for which the tools will create output.

For instance when installing GCC, the GNU Compiler Collection, we can use --target=target to specify that we want to build GCC as a cross-compiler for target. Mixing --build and --target, we can actually cross-compile a cross-compiler; such a three-way cross-compilation is known as a Canadian cross.

See Specifying the System Type, for more information about these configure options.