What is it all about?
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 with the goal to write a clean, efficient and standards-conformant libc implementation. It is designed from scratch to allow efficient static linking and to have realtime-quality robustness by avoiding races, internal failures on resource exhaustion and various other bad worst-case behaviours present in existing implementations.
musl provides consistent quality and implementation behavior from tiny embedded systems to full-fledged servers. Designed from the ground up for static linking, musl carefully avoids pulling in large amounts of code or data that the application will not use. Dynamic linking is also efficient; by integrating the entire standard library implementation, including threads, math, and even the dynamic linker itself into a single shared object, most of the startup time and memory overhead of dynamic linking have been eliminated. musl features the first post-NPTL implementation of POSIX threads for Linux, and the first aimed at complete conformance and robustness. Thread cancellation has been re-designed to avoid serious race conditions in the original NPTL design. As for efficiency, the whole threads implementation weighs in at around 10-20k depending on target architecture and compiler settings.