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TypeTriplets
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System Type Triplets
The Need for System Identification
As mentioned in Cross Compilation Quickstart, the Autotools generated configure script used to simplify cross compilation creates a Makefile customized to your platform and development needs. The configure script tries it's best to figure out what to do, in part, by working with it's friends config.guess and config.sub to guess your platform type.
While the whole process is rather clever and tends to work automagically in many cases, there are situations such as cross compiling where you need to help configure by explicitly identifying your system type. You identify your system type by setting configure's --build, --host, and (sometimes) --target arguments to the correct target triplet values.
Target Triplets and the Configure Script
The target triplet has the form cpu-vendor-os where os can take the form of system or kernel-system. The three command line configure options used to specify system type are:
--build=type
the type of the system used to configure and build the package. Defaults to output of
config.guess.
--host=type
the type of the system on which the built package executes. Defaults to the same type as the build system and enables cross compilation mode.
--target=type
used for building compiler tools for cross compiling. The type of the system for which any compiler tools built from the package produce code for. Defaults to the same type as the host.
To see what configure thinks is the triplet for your build system, simply execute the config.guess script from any source package you may have extracted to your system. For example, on my Windows 7 32-bit Ultimate system with a MSYS Unix-like shell environment installed, the configure used by libxml2, by default, will identify my build system as i686-pc-mingw32.
C:\Users\Jon\Documents\libxml2-2.7.8>sh -c "./config.guess"
i686-pc-mingw32
If you do need to override config.guess, provide a value to configure's --build argument not --host since using --host will cause configure to enter cross compilation mode.
In many cases configure can recognize short aliases for common system type triplets as configure uses the config.sub helper script to canonicalize system type aliases. To see the canonical triplet for a given alias, try something similar to
C:\Users\Jon\Documents>sh -c "./config.sub xbox"
i686-pc-mingw32
C:\Users\Jon\Documents>sh -c "./config.sub mingw32"
i386-pc-mingw32
C:\Users\Jon\Documents>sh -c "./config.sub mac"
m68k-apple-macos
Triplets and MinGW-w64
When using the MinGW-w64 cross compilers, while you may need to use different --build triplets, you will only use the --host triplets i686-w64-mingw32 or x86_64-w64-mingw32. Use i686-w64-mingw32 when building for 32-bit Windows platforms, and x86_64-w64-mingw32 when building for 64-bit Windows platforms. When using the MinGW-w64 native compilers, you typically do not need to provide configure any type triplet information .
