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Date: Sat, 8 Sep 2012 08:07:34 -0700
From: Isaac Dunham <>
Subject: Re: documenting musl

Hello everyone,
I'm glad to see all the helpful discussion about the proper source
format for documentation. :P

Any comments on the _documentation_, as opposed to what format I'm
thinking about putting it into when I think it's ready?
(quoting it did mess up the text formatting, fyi: see the attachment to
my first post if you care.)
> The unofficial musl manual
> Feature test macros, standards:
> Musl supports the following standards, with the given feature test
> macros or parameters: X/Open 2008 (SUS4)	_XOPEN_SOURCE   >= 700
> ISO C99			(requires -std=c99 or equivalent;
> detected using __STRICT_ANSI__, which gcc sets automatically)
> The following standards are partly supported:
> ISO C11			(WIP, threads and atomics aren't
> supported yet, and Annex K is unlikely to be supported in the
> foreseeable future; use -std=c11 or equivalent)
> ANSI C89/ISO C90	A few details are incompatible with C99, and
> the namespace respected is the C99 one.  However, there 
> 			shouldn't be breakage.
> 700 Exposes legacy extensions as well as the modern 
> 			standard, rather than only the legacy
> standard.
> The following feature test macros are also supported to the extent
> practical: _GNU_SOURCE		Partial glibc compatability.
> 			Nonstandard functions with the same names as
> standard ones (basename and several others) ARE NOT SUPPORTED:
> 			musl uses the ISO/POSIX/SUS definition
> unconditionally. _LARGEFILE64_SOURCE	nop: musl only provides
> 64bit file io, so this just adds *64 aliases to the namespace
> _BSD_SOURCE		While glibc is still stuck at BSD 4.4,
> musl provides much of the functionality available via _NETBSD_SOURCE
> 			on NetBSD. This includes strlcpy, strlcat,
> and fgetln.
> By default (-std=gnu* or no arguments for GCC), musl currently sets 
> _XOPEN_SOURCE to 700 and defines _BSD_SOURCE.
> With musl 0.9.4 or older, musl defaulted to ANSI C99.
> Detecting musl:
> This is frequently asked about. It is not possible to detect musl for
> sure. Key differences:
> __linux and __ELF will both be defined, unlike with dietlibc.
> unistd.h defines _XOPEN_VERSION to 700 and _POSIX_VERSION to 200809L. 
> (This is what you should be checking for, unless you need nonstandard
> functions) features.h defaults to defining _BSD_SOURCE and
> _XOPEN_SOURCE, rather than _BSD_SOURCE and _SVID_SOURCE; __USE_*
> macros are not present, nor are the __GLIBC* macros. Using GNU
> basename syntax ( basename("/usr"); ) will make for segfaults.

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