==== Installing musl ==== musl may be installed either as an alternate C library alongside the existing libraries on a system, or as the primary C library for a new or existing musl-based system. First, some prerequisites: - A C99 compiler with gcc-style inline assembly support, support for weak aliases, and support for building stand-alone assembly files. gcc 3.x and 4.x are known to work. pcc and LLVM/clang may work but are untested, and pcc is known to have some bugs. - GNU make - Linux, preferably 2.6.22 or later. Older versions are known to have serious bugs that will make some interfaces non-conformant, but if you don't need threads or POSIX 2008 features, even 2.4 is probably okay. - A supported CPU architecture (currently i386, x86_64, or arm). - If you want to use dynamic linking, it's recommended that you have permissions to write to /lib and /etc. Otherwise your binaries will have to use a nonstandard dynamic linker path. == Option 1: Installing musl as an alternate C library == In this setup, musl and any third-party libraries linked to musl will reside under an alternate prefix such as /usr/local/musl or /opt/musl. A wrapper script for gcc, called musl-gcc, can be used in place of gcc to compile and link programs and libraries against musl. To install musl as an alternate libc, follow these steps: 1. Configure musl's build with a command similar to: ./configure --prefix=/usr/local/musl --exec-prefix=/usr/local Refer to ./configure --help for details on other options. You may change the install prefix if you like, but DO NOT set it to a location that contains your existing libraries based on another libc such as glibc or uClibc. If you do not intend to use dynamic linking, you may disable it at this point via --disable-shared and cut the build time in half. If you wish to use dynamic linking but do not have permissions to write to /lib, you will need to set an alternate dynamic linker location via --syslibdir. 2. Run "make". Parallel build is fully supported, so you can instead use "make -j3" or so on SMP systems if you like. 3. Run "make install" as a user sufficient privileges to write to the destination. 4. Create a file named /etc/ld-musl-$ARCH.path (where $ARCH is replaced by i386, x86_64, etc. as appropriate) containing the correct colon-delimited search path for where you intend to install musl-linked shared library files. If this file is missing, musl will search the standard path, and you will encounter problems when it attempts to load libraries linked against your host libc. Note that this step can be skipped if you disabled dynamic linking. After installing, you can use musl via the musl-gcc wrapper. For example: cat > hello.c < int main() { printf("hello, world!\n"); return 0; } EOF musl-gcc hello.c ./a.out To configure autoconf-based program to compile and link against musl, you may wish to use: CC="musl-gcc -D_GNU_SOURCE" ./configure ... Correctly-written build systems should not need -D_GNU_SOURCE as part of $CC, but many programs do not use feature-test macros correctly and simply assume the compiler will automatically give them the kitchen sink, so the above command is an easy workaround. You will probably also want to use --prefix when building libraries to ensure that they are installed under the musl prefix and not in the main host system library directories. Finally, it's worth noting that musl's include and lib directories in the build tree are setup to be usable without installation, if necessary. Just modify the the paths in the spec file used by musl-gcc (it's located at $prefix/lib/musl-gcc.specs) to point to the source/build tree. == Option 2: Installing musl as the primary C library == In this setup, you will need an existing compiler/toolchain. It shouldnt matter whether it was configured for glibc, uClibc, musl, or something else entirely, but sometimes gcc can be uncooperative, especially if the system distributor has built gcc with strange options. It probably makes the most sense to perform the following steps inside a chroot setup or on a virtualized machine with the filesystem containing just a minimal toolchain. WARNING: DO NOT DO THIS ON AN EXISTING SYSTEM UNLESS YOU REALLY WANT TO CONVERT IT TO BE A MUSL-BASED SYSTEM!! 1. If you are just upgrading an existing version of musl, you can skip step 1 entirely. Otherwise, move the existing include and lib directories on your system out of the way. Unless all the binaries you will need are static-linked, you should edit /etc/ld.so.conf (or equivalent) and put the new locations of your old libraries in the search path before you move them, or your system will break badly and you will not be able to continue. 2. Configure musl's build with a command similar to: ./configure --prefix=/usr --disable-gcc-wrapper Refer to ./configure --help for details on other options. 3. Run "make" to compile musl. 4. Run "make install" with appropriate privileges. 5. If you are using gcc and wish to use dynamic linking, find the gcc directory containing libgcc.a (it should be something like /usr/lib/gcc/i486-linux-gnu/4.3.5, with the arch and version possibly different) and look for a specs file there. If none exists, use "gcc -dumpspecs > specs" to generate a specs file. Find the dynamic linker (/lib/ld-linux.so.2 or similar) and change it to "/lib/ld-musl-$ARCH.so.1" (with $ARCH replaced by your CPU arch). At this point, musl should be the default libc. Compile a small test program with gcc and verify (using readelf -a or objdump -x) that the dynamic linker (program interpreter) is /lib/ld-musl-$ARCH.so.1. If you're using static linking only, you might instead check the symbols and look for anything suspicious that would indicate your old glibc or uClibc was used. When building programs against musl, you may still want to ensure the appropriate feature test macros get defined, as in: CC="gcc -D_GNU_SOURCE" ./configure ...