Rich Felker
41d7c77d6a
the historical mess of having different definitions for C and C++ comes from the historical C definition as (void *)0 and the fact that (void *)0 can't be used in C++ because it does not convert to other pointer types implicitly. however, using plain 0 in C++ exposed bugs in C++ programs that call variadic functions with NULL as an argument and (wrongly; this is UB) expect it to arrive as a null pointer. on 64-bit machines, the high bits end up containing junk. glibc dodges the issue by using a GCC extension __null to define NULL; this is observably non-conforming because a conforming application could observe the definition of NULL via stringizing and see that it is neither an integer constant expression with value zero nor such an expression cast to void. switching to 0L eliminates the issue and provides compatibility with broken applications, since on all musl targets, long and pointers have the same size, representation, and argument-passing convention. we could maintain separate C and C++ definitions of NULL (i.e. just use 0L on C++ and use (void *)0 on C) but after careful analysis, it seems extremely difficult for a C program to even determine whether NULL has integer or pointer type, much less depend in subtle, unintentional ways, on whether it does. C89 seems to have no way to make the distinction. on C99, the fact that (int)(void *)0 is not an integer constant expression, along with subtle VLA/sizeof semantics, can be used to make the distinction, but many compilers are non-conforming and give the wrong result to this test anyway. on C11, _Generic can trivially make the distinction, but it seems unlikely that code targetting C11 would be so backwards in caring which definition of NULL an implementation uses. as such, the simplest path of using the same definition for NULL in both C and C++ was chosen. the #undef directive was also removed so that the compiler can catch and give a warning or error on redefinition if buggy programs have defined their own versions of NULL prior to inclusion of standard headers.
musl libc - a new standard library to power a new generation of
Linux-based devices. musl is lightweight, fast, simple, free, and
strives to be correct in the sense of standards-conformance and
safety.
musl is an alternative to glibc, eglibc, uClibc, dietlibc, and klibc.
For reasons why one might prefer musl, please see the FAQ and libc
comparison chart on the project website,
http://www.musl-libc.org/
For installation instructions, see the INSTALL file.
Please refer to the COPYRIGHT file for details on the copyright and
license status of code included in musl (standard MIT license).
Greetings!
The 0.9.x release series for musl features interface 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. As the release series progresses, we are
gradually adding support for incomplete functionality in existing
interfaces, additional functions that are deemed to be important due
to their use in real-world software, and support for new library and
language features in C11 such as thread-local storage, which is now
supported on all targets. In addition, support for additional target
cpu architectures is being added.
The number of packages build successfully against musl - either
out-of-the-box or with minor patches to address portability errors -
has exceeded 5000 and is steadily growing. In addition to application
compatibility testing, unit testing has been conducted using three
separate test frameworks and numerous additional standalone test cases
to verify the correctness of the implementation.
Included with this package is a gcc wrapper script (musl-gcc) which
allows you to build musl-linked programs using an existing gcc 3.x or
4.x toolchain on the host. There are also now at several mini
distributions (in the form of build scripts) which provide a
self-hosting musl-based toolchain and system root. These are much
better options than the wrapper script if you wish to use dynamic
linking or build packages with many library dependencies. See the musl
website for details.
The musl project is actively seeking contributors, mostly in the areas
of porting, testing, and application compatibility improvement. For
bug reports, support requests, or to get involved in development,
please visit #musl on Freenode IRC or subscribe to the musl mailing
list by sending a blank email to musl-subscribe AT lists DOT openwall
DOT com.
Thank you for using musl.
Cheers,
Rich Felker / dalias