Quick Installation Guide for musl libc ====================================== There are many different ways to install musl depending on your usage case. This document covers only the build and installation of musl by itself, which is useful for upgrading an existing musl-based system or compiler toolchain, or for using the provided musl-gcc wrapper with an existing non-musl-based compiler. Building complete native or cross-compiler toolchains is outside the scope of this INSTALL file. More information can be found on the musl website and community wiki. Build Prerequisites ------------------- The only build-time prerequisites for musl are GNU Make and a freestanding C99 compiler toolchain targeting the desired instruction set architecture and ABI, with support for gcc-style inline assembly, weak aliases, and stand-alone assembly source files. The system used to build musl does not need to be Linux-based, nor do the Linux kernel headers need to be available. If support for dynamic linking is desired, some further requirements are placed on the compiler and linker. In particular, the linker must support the -Bsymbolic-functions option. At present, GCC 4.6 or later is the recommended compiler for building musl. Any earlier version of GCC with full C99 support should also work, but may be subject to minor floating point conformance issues on i386 targets. Sufficiently recent versions of PCC and LLVM/clang are also believed to work, but have not been tested as heavily; prior to Fall 2012, both had known bugs that affected musl. Firm/cparser is also believed to work but lacks support for producing shared libraries. GCC 4.9.0 and 4.9.1 are known to have a serious bug (#61144) which affects musl. Beginning with version 1.1.4 musl attempts to work around the bug, but these compiler versions are still considered unstable and unsupported. Supported Targets ----------------- musl can be built for the following CPU instruction set architecture and ABI combinations: * i386 * Minimum CPU model is actually 80486 unless kernel emulation of the `cmpxchg` instruction is added * x86_64 * ARM * EABI, standard or hard-float VFP variant * Little-endian default; big-endian variants also supported * Compiler toolchains only support armv4t and later * MIPS * ABI is o32 * Big-endian default; little-endian variants also supported * Default ABI variant uses FPU registers; alternate soft-float ABI that does not use FPU registers or instructions is available * MIPS2 or later, or kernel emulation of ll/sc (standard in Linux) is required * PowerPC * Only 32-bit is supported * Compiler toolchain must provide 64-bit long double, not IBM double-double or IEEE quad * For dynamic linking, compiler toolchain must be configured for "secure PLT" variant * Microblaze * Big-endian default; little-endian variants also supported * Soft-float * Requires support for lwx/swx instructions The following additional targets are available for build, but may not work correctly and may not yet have ABI stability: * SuperH (SH) * Little-endian by default; big-engian variant also supported * Full FPU ABI or soft-float ABI is supported, but the single-precision-only FPU ABI is not supported (musl always requires IEEE single and double to be supported) * x32 (x86_64 ILP32 ABI) Build and Installation Procedure -------------------------------- To build and install musl: 1. Run the provided configure script from the top-level source directory, passing on its command line any desired options. 2. Run "make" to compile. 3. Run "make install" with appropriate privileges to write to the target locations. The configure script attempts to determine automatically the correct target architecture based on the compiler being used. For some compilers, this may not be possible. If detection fails or selects the wrong architecture, you can provide an explicit selection on the configure command line. By default, configure installs to a prefix of "/usr/local/musl". This differs from the behavior of most configure scripts, and is chosen specifically to avoid clashing with libraries already present on the system. DO NOT set the prefix to "/usr", "/usr/local", or "/" unless you're upgrading libc on an existing musl-based system. Doing so will break your existing system when you run "make install" and it may be difficult to recover. Notes on Dynamic Linking ------------------------ If dynamic linking is enabled, one file needs to be installed outside of the installation prefix: /lib/ld-musl-$ARCH.so.1. This is the dynamic linker. Its pathname is hard-coded into all dynamic-linked programs, so for the sake of being able to share binaries between systems, a consistent location should be used everywhere. Note that the same applies to glibc and its dynamic linker, which is named /lib/ld-linux.so.2 on i386 systems. If for some reason it is impossible to install the dynamic linker in its standard location (for example, if you are installing without root privileges), the --syslibdir option to configure can be used to provide a different location At runtime, the dynamic linker needs to know the paths to search for shared libraries. You should create a text file named /etc/ld-musl-$ARCH.path (where $ARCH matches the architecture name used in the dynamic linker) containing a list of directories where you want the dynamic linker to search for shared libraries, separated by colons or newlines. If the dynamic linker has been installed in a non-default location, the path file also needs to reside at that location (../etc relative to the chosen syslibdir). If you do not intend to use dynamic linking, you may disable it by passing --disable-shared to configure; this also cuts the build time in half. Checking for Successful Installation ------------------------------------ After installing, you should be able to use musl via the musl-gcc wrapper. For example: cat > hello.c < int main() { printf("hello, world!\n"); return 0; } EOF /usr/local/musl/bin/musl-gcc hello.c ./a.out To configure autoconf-based program to compile and link against musl, set the CC variable to musl-gcc when running configure, as in: CC=musl-gcc ./configure ... 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.