Musl

musl

musl

musl ldd command output.
Release Status	Maintained
Last Release	1.2.5 (2024-02-29, commit[2])
Language(s)	C
Developer(s)	Rich Felker (dalias) and others
Website	musl.libc.org

musl is a C standard library intended for operating systems based on the Linux kernel, released under the MIT License. It was developed by Rich Felker to write a clean, efficient, and standards-conformant libc implementation.

Usage on Operating Systems

Linux distributions which use musl as their standard C library (some use only musl) include but are not limited to:

• Alpine Linux
• Dragora 3
• Gentoo Linux (glibc by default, musl can be chosen at install time)
• OpenWrt
• postmarketOS
• Sabotage
• Morpheus Linux
• Chimera Linux
• Void Linux

The seL4 microkernel ships with musl, for binaries that have been linked against glibc, gcompat, glibmus-hq. can be used to execute them on musl-based distros.

Comparisons between different C library implementations.

Bloat comparison	musl	uClibc	dietlibc	glibc
Complete .a set	426k	500k	120k	2.0M †
Complete .so set	527k	560k	185k	7.9M †
Smallest static C program	1.8k	5k	0.2k	662k
Static hello (using printf)	13k	70k	6k	662k
Dynamic overhead (min. dirty)	20k	40k	40k	48k
Static overhead (min. dirty)	8k	12k	8k	28k
Static stdio overhead (min. dirty)	8k	24k	16k	36k
Configurable featureset	no	yes	minimal	minimal
Behavior on resource exhaustion	musl	uClibc	dietlibc	glibc
Thread-local storage	reports failure	aborts	n/a	aborts
SIGEV_THREAD timers	no failure	n/a	n/a	lost overruns
pthread_cancel	no failure	aborts	n/a	aborts
regcomp and regexec	reports failure	crashes	reports failure	crashes
fnmatch	no failure	unknown	no failure	reports failure
printf family	no failure	no failure	no failure	reports failure
strtol family	no failure	no failure	no failure	no failure
Performance comparison	musl	uClibc	dietlibc	glibc
Tiny allocation & free	0.005	0.004	0.013	0.002
Big allocation & free	0.027	0.018	0.023	0.016
Allocation contention, local	0.048	0.134	0.393	0.041
Allocation contention, shared	0.050	0.132	0.394	0.062
Zero-fill (memset)	0.023	0.048	0.055	0.012
String length (strlen)	0.081	0.098	0.161	0.048
Byte search (strchr)	0.142	0.243	0.198	0.028
Substring (strstr)	0.057	1.273	1.030	0.088
Thread creation/joining	0.248	0.126	45.761	0.142
Mutex lock/unlock	0.042	0.055	0.785	0.046
UTF-8 decode buffered	0.073	0.140	0.257	0.351
UTF-8 decode byte-by-byte	0.153	0.395	0.236	0.563
Stdio putc/getc	0.270	0.808	7.791	0.497
Stdio putc/getc unlocked	0.200	0.282	0.269	0.144
Regex compile	0.058	0.041	0.014	0.039
Regex search (a{25}b)	0.188	0.188	0.967	0.137
Self-exec (static linked)	234µs	245µs	272µs	457µs
Self-exec (dynamic linked)	446µs	590µs	675µs	864µs
ABI and versioning comparison	musl	uClibc	dietlibc	glibc
Stable ABI	yes	no	unofficially	yes
LSB-compatible ABI	incomplete	no	no	yes
Backwards compatibility	yes	no	unofficially	yes
Forwards compatibility	yes	no	unofficially	no
Atomic upgrades	yes	no	no	no
Symbol versioning	no	no	no	yes
Algorithms comparison	musl	uClibc	dietlibc	glibc
Substring search (strstr)	twoway	naive	naive	twoway
Regular expressions	dfa	dfa	backtracking	dfa
Sorting (qsort)	smoothsort	shellsort	naive quicksort	introsort
Allocator (malloc)	musl-native	dlmalloc	diet-native	ptmalloc
Features comparison	musl	uClibc	dietlibc	glibc
Conformant printf	yes	yes	no	yes
Exact floating point printing	yes	no	no	yes
C99 math library	yes	partial	no	yes
C11 threads API	yes	no	no	no
C11 thread-local storage	yes	yes	no	yes
GCC libstdc++ compatibility	yes	yes	no	yes
POSIX threads	yes	yes, on most archs	broken	yes
POSIX process scheduling	stub	incorrect	no	incorrect
POSIX thread priority scheduling	yes	yes	no	yes
POSIX localedef	no	no	no	yes
Wide character interfaces	yes	yes	minimal	yes
Legacy 8-bit codepages	no	yes	minimal	slow, via gconv
Legacy CJK encodings	no	no	no	slow, via gconv
UTF-8 multibyte	native; 100% conformant	native; nonconformant	dangerously nonconformant	slow, via gconv; nonconformant
Iconv character conversions	most major encodings	mainly UTFs	no	the kitchen sink
Iconv transliteration extension	no	no	no	yes
Openwall-style TCB shadow	yes	no	no	no
Sun RPC, NIS	no	yes	yes	yes
Zoneinfo (advanced timezones)	yes	no	yes	yes
Gmon profiling	no	no	yes	yes
Debugging features	no	no	no	yes
Various Linux extensions	yes	yes	partial	yes
Target architectures comparison	musl	uClibc	dietlibc	glibc
i386	yes	yes	yes	yes
x86_64	yes	yes	yes	yes
x86_64 x32 ABI (ILP32)	experimental	no	no	non-conforming
ARM	yes	yes	yes	yes
Aarch64 (64-bit ARM)	yes	no	no	yes
MIPS	yes	yes	yes	yes
SuperH	yes	yes	no	yes
Microblaze	yes	partial	no	yes
PowerPC (32- and 64-bit)	yes	yes	yes	yes
Sparc	no	yes	yes	yes
Alpha	no	yes	yes	yes
S/390 (32-bit)	no	no	yes	yes
S/390x (64-bit)	yes	no	yes	yes
OpenRISC 1000 (or1k)	yes	no	no	not upstream
Motorola 680x0 (m68k)	yes	yes	no	yes
MMU-less microcontrollers	yes, elf/fdpic	yes, bflt	no	no
Build environment comparison	musl	uClibc	dietlibc	glibc
Legacy-code-friendly headers	partial	yes	no	yes
Lightweight headers	yes	no	yes	no
Usable without native toolchain	yes	no	yes	no
Respect for C namespace	yes	LFS64 problems	no	LFS64 problems
Respect for POSIX namespace	yes	LFS64 problems	no	LFS64 problems
Security/hardening comparison	musl	uClibc	dietlibc	glibc
Attention to corner cases	yes	yes	no	too much malloc
Safe UTF-8 decoder	yes	yes	no	yes
Avoids superlinear big-O's	yes	sometimes	no	yes
Stack smashing protection	yes	yes	no	yes
Heap corruption detection	yes	no	no	yes
Misc. comparisons	musl	uClibc	dietlibc	glibc
License	MIT	LGPL 2.1	GPL 2	LGPL 2.1+ w/exceptions

Official benchmarks

See also

• Bionic libc
• dietlibc
• Glibc
• klibc
• Newlib
• uClibc