LLVM Cross-Compiler

Difficulty level
Advanced

EDIT: A mostly working Clang cross-compiler is generated by this buildscript. Dissect it to learn more. TODO: move details to this page.

Is as simple as that:

mkdir crossllvm
cd crossllvm
svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm
cd llvm/tools
svn co http://llvm.org/svn/llvm-project/cfe/trunk clang
cd ../..
mkdir build
cd build
cmake ../llvm
make

After building you will have a compiler able to output multiple output formats regardless of your current platform, you can specify x86 ELF output format (for example) to clang using "-ccc-host-triple i686-pc-linux-gnu".

TODO: beware that clang is both a cross-compiler and a host-compiler and you would have to specify some options to disable host functionality.

TODO: clang requires a fairly recent version of binutils to work, try 2.21 or above if you get assembly compilation errors.

TODO: describe non-svn build from released tarballs.

TODO: integrate libc++ build instructions

pitfall@osdev.forum wrote:

As far as I know, you can use -ccc-host-triple <your target output format> option with -march=<your target architecture> to cross-compile with LLVM. It's been a while since I used LLVM/CLang, but I think this'll work with some investigation.

Here's an example quoted for some obscure mailing lists illustrating what I wrote :

-march=armv7-a -mfloat-abi=soft -ccc-host-triple arm-elf

JamesM@osdev.forum wrote:

Or since 3.1 you can just shorten this to:

-target armv7--eabi -mcpu=cortex-a9

It is recommended to build post-3.1 clang as there are some crash bugs fixed.