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glaucus

musl

  • Depends on mawk
  • install-tools is for the wrapper musl-gcc
  • Do not set the prefix to /usr, /usr/local, or / unless upgrading libc on an existing musl-based system (this will break your existing system after running make install making it difficult to recover)
  • The dynamic linker searches for shared libraries at run time under directories listed in /etc/ld-musl-$ARCH.path separated by colons or newlines
  • If the dynamic linker has been installed in a non-default location, the path needs to reside at that location (../etc relative to the chosen syslibdir)
  • Do not use --syslibdir=/usr/lib as it will break the ABI; /lib/ld-musl-x86_64.so.1 gets hardcoded in the binaries regardless of syslibdir (You can check with readelf -p .interp /bin/toybox)
  • DT_RELR support (-z pack-relative-relocs) has been upstreamed, and reduces size by 5 - 8%
  • Does musl conflict/replace libssp (the standalone package)
  • gencat requires queue.h
  • Alpaquita statically links against glibc-string; a library that provides extra performance optimizations for string manipulation and memory functions
  • Alpaquita has patches to fix ldd output for static-pie executables
  • Chimera surgically removes musl’s malloc-ng and replaces it with mimalloc
  • LC_ALL overrides category-specific variables, and LANG provides a default for any category not set
  • MUSL_LOCPATH - Colon-separated list of paths that will be searched for locale definitions. The requested locale name string will used as a filename and searched in each path component. If unset, locale files are not loaded and only the “C” locale is available. This variable is completely ignored in programs invoked setuid, setgid, or with other elevated capabilities
  • musl provides empty crti.o and crtn.o for legacy .init and .fini support; use .init_array and .fini_array instead as they are the modern implementation (this means that gcc and binutils should be configured with --enable-initfini-array)
  • Log messages will be discarded if /dev/log is absent
  • musl treats all text as UTF-8, and all non-ASCII characters as first-class; no external locale files or conversion modules are needed
  • musl does not support DNS for non-ASCII domains (IDN); not complete yet but will be supported in the future
  • In the absence of the LANG and LC_* environment variables, POSIX leaves the default locale (used when "" is passed to setlocale) implementation-defined. Under glibc versions at least up through 2.26, this default is “C”. musl on the other hand always uses “C.UTF-8” as the default. There has been discussion on the glibc side of possibly adopting the musl behavior here once the “C.UTF-8” locale is an established feature of glibc.
  • musl’s resolver queries nameservers in parallel and accepts whichever response arrives first
  • This can increase network load and is mitigated by only supporting up to three nameservers:
    • Caching nameserver on localhost (near-zero latency for locally cached results, but typically smallest cache size, and slowest for queries not serviceable from cache)
    • ISP nameserver (very low latency for cached results, typically moderate cache size, and moderate performance for queries not serviceable from cache)
    • 8.8.8.8 (somewhat higher latency but tends to have the whole DNS tree cached)
  • LD_PRELOAD and LD_LIBRARY_PATH are completely ignored in programs that invoke setuid, setgid, or with other elevated capabilities
  • musl recommends building with recent versions of gcc (see INSTALL)
  • Linux kernel headers are not required to build musl, and might even collide with musl headers
  • musl does not implement legacy functions operating on ucontext_t (getcontext, setcontext, makecontext, swapcontext); no longer part of POSIX, but cooperative multi-tasking applications use them, ucontext_t also appears as an argument to sigaction handlers which cannot be used portably

References

Section titled “References”