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musl - an implementation of the standard library for Linux-based systems
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Rich Felker 188759bbee overhaul shared library ctor execution for dependency order, concurrency 
previously, shared library constructors at program start and dlopen
time were executed in reverse load order. some libraries, however,
rely on a depth-first dependency order, which most other dynamic
linker implementations provide. this is a much more reasonable, less
arbitrary order, and it turns out to have much better properties with
regard to how slow-running ctors affect multi-threaded programs, and
how recursive dlopen behaves.

this commit builds on previous work tracking direct dependencies of
each dso (commit 4035556907), and
performs a topological sort on the dependency graph at load time while
the main ldso lock is held and before success is committed, producing
a queue of constructors needed by the newly-loaded dso (or main
application). in the case of circular dependencies, the dependency
chain is simply broken at points where it becomes circular.

when the ctor queue is run, the init_fini_lock is held only for
iteration purposes; it's released during execution of each ctor, so
that arbitrarily-long-running application code no longer runs with a
lock held in the caller. this prevents a dlopen with slow ctors in one
thread from arbitrarily delaying other threads that call dlopen.
fully-independent ctors can run concurrently; when multiple threads
call dlopen with a shared dependency, one will end up executing the
ctor while the other waits on a condvar for it to finish.

another corner case improved by these changes is recursive dlopen
(call from a ctor). previously, recursive calls to dlopen could cause
a ctor for a library to be executed before the ctor for its
dependency, even when there was no relation between the calling
library and the library it was loading, simply due to the naive
reverse-load-order traversal. now, we can guarantee that recursive
dlopen in non-circular-dependency usage preserves the desired ctor
execution order properties, and that even in circular usage, at worst
the libraries whose ctors call dlopen will fail to have completed
construction when ctors that depend on them run.

init_fini_lock is changed to a normal, non-recursive mutex, since it
is no longer held while calling back into application code.
2019-03-03 12:06:22 -05:00
arch move arch-invariant definitions out of bits/ioctl.h 2019-02-07 12:43:19 -05:00
crt define and use internal macros for hidden visibility, weak refs 2018-09-05 14:05:14 -04:00
dist add another example option to dist/config.mak 2012-04-24 16:49:11 -04:00
include add membarrier syscall wrapper, refactor dynamic tls install to use it 2019-02-22 03:25:39 -05:00
ldso overhaul shared library ctor execution for dependency order, concurrency 2019-03-03 12:06:22 -05:00
src add membarrier syscall wrapper, refactor dynamic tls install to use it 2019-02-22 03:25:39 -05:00
tools fix musl-gcc wrapper to be compatible with default-pie gcc toolchains 2018-08-02 19:15:48 -04:00
.gitignore remove obsolete gitignore rules 2016-07-06 00:21:25 -04:00
configure configure: accept ppc[64] as alias for powerpc[64] in gcc tuples 2019-01-19 18:39:54 -05:00
COPYRIGHT new tsearch implementation 2018-09-20 17:57:47 -04:00
dynamic.list fix regression in access to optopt object 2018-11-19 13:20:41 -05:00
INSTALL add powerpc64 and s390x to list of supported archs in INSTALL file 2017-08-29 20:48:02 -04:00
Makefile overhaul internally-public declarations using wrapper headers 2018-09-12 14:34:33 -04:00
README update version reference in the README file 2014-06-25 14:16:53 -04:00
VERSION release 1.1.21 2019-01-21 12:30:47 -05:00
WHATSNEW release 1.1.21 2019-01-21 12:30:47 -05:00

README 

    musl libc

musl, pronounced like the word "mussel", is an MIT-licensed
implementation of the standard C library targetting the Linux syscall
API, suitable for use in a wide range of deployment environments. musl
offers efficient static and dynamic linking support, lightweight code
and low runtime overhead, strong fail-safe guarantees under correct
usage, and correctness in the sense of standards conformance and
safety. musl is built on the principle that these goals are best
achieved through simple code that is easy to understand and maintain.

The 1.1 release series for musl features coverage for all interfaces
defined in ISO C99 and POSIX 2008 base, along with a number of
non-standardized interfaces for compatibility with Linux, BSD, and
glibc functionality.

For basic installation instructions, see the included INSTALL file.
Information on full musl-targeted compiler toolchains, system
bootstrapping, and Linux distributions built on musl can be found on
the project website:

    http://www.musl-libc.org/