exit(3): make it thread-safe

(cherry picked from commit 3f3ec4b99f79d32a0bf15495559ca9883bd751f2)

libc: Purge unneeded cdefs.h

These sys/cdefs.h are not needed. Purge them. They are mostly left-over
from the $FreeBSD$ removal. A few in libc are still required for macros
that cdefs.h defines. Kee

libc: Purge unneeded cdefs.h

These sys/cdefs.h are not needed. Purge them. They are mostly left-over
from the $FreeBSD$ removal. A few in libc are still required for macros
that cdefs.h defines. Keep those.

Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D42385

(cherry picked from commit 559a218c9b257775fb249b67945fe4a05b7a6b9f)

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Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

General further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 3-Clause license.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier f

General further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 3-Clause license.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

Special thanks to Wind River for providing access to "The Duke of
Highlander" tool: an older (2014) run over FreeBSD tree was useful as a
starting point.

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Add __cxa_thread_atexit(3) API implementation.

This is the backing feature to implement C++11 thread storage duration
specified by the thread_local keyword. A destructor for given
thread-local obje

Add __cxa_thread_atexit(3) API implementation.

This is the backing feature to implement C++11 thread storage duration
specified by the thread_local keyword. A destructor for given
thread-local object is registered to be executed at the thread
termination time using __cxa_thread_atexit(). Libc calls the
__cxa_thread_calls_dtors() during exit(3), before finalizers and
atexit functions, and libthr calls the function at the thread
termination time, after the stack unwinding and thread-specific key
destruction.

There are several uncertainties in the API which lacks a formal
specification. Among them:
- is it allowed to register destructors during destructing;
we allow, but limiting the nesting level. If too many iterations
detected, a diagnostic is issued to stderr and thread forcibly
terminates for now.
- how to handle destructors which belong to an unloading dso;
for now, we ignore destructor calls for such entries, and
issue a diagnostic. Linux does prevent dso unload until all
threads with destructors from the dso terminated.
It is supposed that the diagnostics allow to detect real-world
applications relying on the above details and possibly adjust
our implementation. Right now the choices were to provide the slim
API (but that rarely stands the practice test).

Tests are added to check generic functionality and to specify some of
the above implementation choices.

Submitted by: Mahdi Mokhtari <mokhi64_gmail.com>
Reviewed by: theraven
Discussed with: dim (detection of -std=c++11 supoort for tests)
Sponsored by: The FreeBSD Foundation (my involvement)
MFC after: 2 weeks
Differential revisions: https://reviews.freebsd.org/D7224,
https://reviews.freebsd.org/D7427

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Use ANSI C prototypes. Eliminates -Wold-style-definition warnings.

Renumber clauses to reduce diffs to other versions

NetBSD, OpenBSD, and Android's Bionic number the clauses 1 through 3,
so follow suit to make comparison easier.

Per Regents of the University of Calfornia letter, remove advertising
clause.

# If I've done so improperly on a file, please let me know.

Move the declaration of __cleanup to libc_private.h as it is used in both
stdio/ and stdlib/. Don't define __cleanup twice.

Implement __cxa_atexit/__cxa_finalize as specified by the cross-vendor
ó++ ABI document at http://www.codesourcery.com/cxx-abi/abi.html#dso-dtor

The ABI was initially defined for ia64, but GCC3 and

Implement __cxa_atexit/__cxa_finalize as specified by the cross-vendor
ó++ ABI document at http://www.codesourcery.com/cxx-abi/abi.html#dso-dtor

The ABI was initially defined for ia64, but GCC3 and Intel compilers
have adopted it on other platforms.

This is the patch from PR bin/59552 with a number of changes by
me.

PR: bin/59552
Submitted by: Bradley T Hughes (bhughes at trolltech dot com)

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Fix the style of the SCM ID's.
I believe have made all of libc .c's as consistent as possible.

Remove 'register' keyword.

Remove _THREAD_SAFE and make libc thread-safe by default by
adding (weak definitions to) stubs for some of the pthread
functions. If the threads library is linked in, the real
pthread functions will

Remove _THREAD_SAFE and make libc thread-safe by default by
adding (weak definitions to) stubs for some of the pthread
functions. If the threads library is linked in, the real
pthread functions will pulled in.

Use the following convention for system calls wrapped by the
threads library:
__sys_foo - actual system call
_foo - weak definition to __sys_foo
foo - weak definition to __sys_foo

Change all libc uses of system calls wrapped by the threads
library from foo to _foo. In order to define the prototypes
for _foo(), we introduce namespace.h and un-namespace.h
(suggested by bde). All files that need to reference these
system calls, should include namespace.h before any standard
includes, then include un-namespace.h after the standard
includes and before any local includes. <db.h> is an exception
and shouldn't be included in between namespace.h and
un-namespace.h namespace.h will define foo to _foo, and
un-namespace.h will undefine foo.

Try to eliminate some of the recursive calls to MT-safe
functions in libc/stdio in preparation for adding a mutex
to FILE. We have recursive mutexes, but would like to avoid
using them if possible.

Remove uneeded includes of <errno.h> from a few files.

Add $FreeBSD$ to a few files in order to pass commitprep.

Approved by: -arch

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Reference an external variable in threaded programs so that the
autoinitialiser gets linked in and therefore called before main().

Add a global variable called __isthreaded that can be tested throughout
libc to determine if locking is required. This is needed in libc
for use with kernel threads, but until a thread is created, we

Add a global variable called __isthreaded that can be tested throughout
libc to determine if locking is required. This is needed in libc
for use with kernel threads, but until a thread is created, we don't
really want to bother locking things. The variable was added here
because the crt code calls exit(main()) so all programs will get the
variable.

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BSD 4.4 Lite Lib Sources