stoked-security/musl-cross

A small suite of scripts and patches for building musl libc cross compilers.

About musl-cross

This is a small suite of scripts and patches to build a musl libc cross-compiler. Prebuilt cross and native compilers are available at http://musl.codu.org/

For the impatient, ./build.sh should build a cross compiler to /opt/cross/-linux-musl, no muss, no fuss. Otherwise, you can edit config.sh to make cross-compilers to other architectures, and even copy config.sh to another directory then run build.sh from there to avoid polluting the source dir.

Project Scope

Supported are GCC 4.0.3 until 5.3.0. for newer GCCs check out the musl-cross-make project.

Notes on building normal cross compilers

• For ARM, you must set the triple to arm-linux-musleabi (eabi is the important bit here)

• You can set versions of binutils, GCC or musl in config.sh with:

    BINUTILS_VERSION=<version>
    GCC_VERSION=<version>
    MUSL_VERSION=<version>
  

• You can set configure flags for each step:

    BINUTILS_CONFFLAGS=...
    GCC_BOOTSTRAP_CONFFLAGS=...
    MUSL_CONFFLAGS=...
    GCC_CONFFLAGS=...
  

• You can use a git checkout of musl with:

    MUSL_VERSION=<git tag or commit>
    MUSL_GIT=yes
  

• If you do not have the GMP, MPFR and/or MPC development libraries on your host, you can build them along with GCC with a config.sh line:

    GCC_BUILTIN_PREREQS=yes
  

Recommendations

• If you would like to target a specific CPU revision, usually this is done by GCC configuration options like so:

    GCC_BOOTSTRAP_CONFFLAGS="--with-cpu=armv4t"
    GCC_CONFFLAGS="--with-cpu=armv4t"
  

  For ix86 however, it is more common to do this by the target name, e.g. i486-linux-musl instead of i686-linux-musl.

Upgrading cross compilers

It is possible to upgrade the musl version in a musl-cross cross compiler without rebuilding the entire cross compiler prefix from scratch. Simply download and extract the new version of musl, then configure it like so:

./configure --prefix="<prefix>/<triple>" CC="<triple>-gcc"

Where "" is the prefix the cross compiler root was installed/extracted to, and is the GNU-style target triple (e.g. i486-linux-musl).

Other scripts and helpers

• config.sh is an example configuration file. In many cases, it will do exactly what you want it to do with no modification, which is why it's simply named "config.sh" instead of, e.g., "config-sample.sh"

• extra/build-gcc-deps.sh will build the dependencies for GCC into the build prefix specified by config.sh, which are just often a nice thing to have. It is of course not necessary.

• extra/build-tarballs.sh builds convenient musl cross-compiler tarballs in a rather inconvenient way. It first builds a musl cross-compiler to the host platform (e.g. i686), then it uses that to build static cross-compilers to various platforms. As a result, building e.g. three cross-compiler tarballs involves eight compiler build phases (read: this is slow). However, the resultant tarballs are cross-compilers statically linked against musl, making them stable and portable.

• config-static.sh is an example configuration file for building a static cross-compiler. You can use this if, e.g., you already have a build of musl (and so have musl-gcc) but would like to make a complete, static cross-compiler based on that, or if you already have a musl cross-compiler (and so have -linux-musl-gcc) but would like to make a static cross-compiler itself compiled against musl.

Requirements

musl-cross depends on:

• shell and core utils (busybox is fine)
• mercurial or git (for checkout only)
• wget (busybox is fine)
• patch
• gcc
• make
• gawk

The following are GCC dependencies, which can be installed on the host system, or installed automatically using GCC_BUILTIN_PREREQS=yes:

• gmp
• mpfr
• mpc

Building GMP additionally requires m4.

Other sources

The patches for GCC are maintained in a separate repository, http://bitbucket.org/GregorR/musl-gcc-patches/ (mirrored to git at http://github.com/GregorR/musl-gcc-patches ).

Compiler/Arch Compatibility Matrix

	i?86	x86_64	x32	mips	powerpc	armv7	microblaze	sh4	or1k
4.7.4	yes	yes		yes	yes	yes
4.8.5	yes	yes	yes	yes	yes	yes	yes	yes
4.9.3	yes	yes	yes	yes	yes	yes	yes	yes
5.3.0	yes	yes	yes	yes	yes	yes	yes	yes	*

• or1k requires integration of a patch (issue #61)