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 (autoconf)Specifying Names section `Specifying the System Type' in The Autoconf Manual, for more information about these configure options.