-==== Installing musl ====
+Quick Installation Guide for musl libc
+======================================
-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.
+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.
-First, some prerequisites:
+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.
-- 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
+Build Prerequisites
+-------------------
-- 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.
+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 a minimal subset of "GNU C"
+extensions consisting mainly of gcc-style inline assembly, weak
+aliases, hidden visibility, and stand-alone assembly source files.
-- A supported CPU architecture (currently i386, x86_64, or arm).
+GCC, LLVM/clang, Firm/cparser, and PCC have all successfully built
+musl, but GCC is the most widely used/tested. Recent compiler (and
+binutils) versions should be used if possible since some older
+versions have bugs which affect musl.
-- 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.
+The system used to build musl does not need to be Linux-based, nor do
+the Linux kernel headers need to be available.
-== Option 1: Installing musl as an alternate C library ==
+Supported Targets
+-----------------
-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.
+musl can be built for the following CPU instruction set architecture
+and ABI combinations:
-To install musl as an alternate libc, follow these steps:
+* i386
+ * Minimum CPU model is actually 80486 unless kernel emulation of
+ the `cmpxchg` instruction is added
-1. Edit config.mak to select your system's CPU architecture (i386,
- x86_64, or arm), installation prefix, location for the dynamic
- linker, and other build preferences.
+* x86_64
+ * ILP32 ABI (x32) is available as a separate arch but is still
+ experimental
-2. Run "make". Parallel build is fully supported, so you can instead
- use "make -j3" or so on SMP systems if you like.
+* ARM
+ * EABI, standard or hard-float VFP variant
+ * Little-endian default; big-endian variants also supported
+ * Compiler toolchains only support armv4t and later
-3. Run "make install" as a user sufficient privileges to write to the
- destination.
+* AArch64
+ * Little-endian default; big-endian variants also supported
-4. Ensure that /etc/ld-musl-$ARCH.path (where $ARCH is replaced by
- i386, x86_64, etc. as appropriate) contains the correct search path
- for where you intend to install musl-linked shared library files.
- This step can be skipped if you disabled dynamic linking.
+* MIPS
+ * ABI is o32, fp32/fpxx (except on r6 which is fp64)
+ * 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
+ * MIPS32r6, an incompatible ISA, is supported as a variant "mipsr6"
-After installing, you can use musl via the musl-gcc wrapper. For
-example:
+* MIPS64
+ * ABI is n64 (LP64) or n32 (ILP32)
+ * 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
-cat > hello.c <<EOF
-#include <stdio.h>
-int main()
-{
- printf("hello, world!\n");
- return 0;
-}
-EOF
-musl-gcc hello.c
-./a.out
+* PowerPC
+ * 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
-To configure autoconf-based program to compile and link against musl,
-you may wish to use:
+* PowerPC64
+ * Both little and big endian variants are supported
+ * Compiler toolchain must provide 64-bit long double, not IBM
+ double-double or IEEE quad
+ * Compiler toolchain must use the new (ELFv2) ABI regardless of
+ whether it is for little or big endian
-CC="musl-gcc -D_GNU_SOURCE" ./configure ...
+* S390X (64-bit S390)
-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.
+* SuperH (SH)
+ * Standard ELF ABI or FDPIC ABI (shared-text without MMU)
+ * 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
-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.
+* Microblaze
+ * Big-endian default; little-endian variants also supported
+ * Soft-float
+ * Requires support for lwx/swx instructions
+
+* OpenRISC 1000 (or1k)
+
+* RISC-V 64
+ * Little endian
+ * Hard, soft, and hard-single/soft-double floating point ABIs
+ * Standard ELF; no shared-text NOMMU support
+
+
+
+Build and Installation Procedure
+--------------------------------
+
+To build and install musl:
-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 musl-gcc wrapper's libc_prefix variable to
-point to the source/build tree.
+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.
-== Option 2: Installing musl as the primary C library ==
+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.
-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.
+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.
-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. Edit musl's config.mak and set the installation prefix to the
- prefix your compiler toolchain is configured to search, probably
- /usr. Set ARCH to match your CPU architecture, and change any other
- options as you see fit.
+Notes on Dynamic Linking
+------------------------
-3. Run "make" to compile musl.
+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.
-4. Run "make install" with appropriate privileges.
+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
-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 $ARCH replaced by your CPU arch).
+At runtime, the dynamic linker needs to know the paths to search for
+shared libraries. You should create a text file named
+/etc/ld-musl-$ARCH.path (where $ARCH matches the architecture name
+used in the dynamic linker) containing a list of directories where you
+want the dynamic linker to search for shared libraries, separated by
+colons or newlines. If the dynamic linker has been installed in a
+non-default location, the path file also needs to reside at that
+location (../etc relative to the chosen syslibdir).
-At this point, musl should be the default libc. Compile a small test
-program with gcc and verify (using readelf -a or objdump -x) that the
-dynamic linker (program interpreter) is /lib/ld-musl-$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.
+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.
-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 ...
+Checking for Successful Installation
+------------------------------------
+
+After installing, you should be able to use musl via the musl-gcc
+wrapper. For example:
+
+cat > hello.c <<EOF
+#include <stdio.h>
+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.
projects / oweals / musl.git / blobdiff