Newlib build system defines __SINGLE_THREAD__ to allow concurrency code
to be only compiled when newlib is configured for multithread. One such
example are locks which become useless in single thread mode. Although
most static locks are indeed guarded by !defined(__SINGLE_THREAD__),
some are not.
This commit adds these missing guards to __dd_hash_mutex,
__atexit_recursive_mutex, __at_quick_exit_mutex and __arc4random_mutex.
It also makes sure locking macros in lock.h are noop in single thread
mode.
According to the OpenBSD man page, "A Replacement Call for Random". It
offers high quality random numbers derived from input data obtained by
the OpenBSD specific getentropy() system call which is declared in
<unistd.h> and must be implemented for each Newlib port externally. The
arc4random() functions are used for example in LibreSSL and OpenSSH.
Cygwin provides currently its own implementation of the arc4random
family. Maybe it makes sense to use this getentropy() implementation:
http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/lib/libcrypto/crypto/getentropy_win.c?rev=1.4&content-type=text/x-cvsweb-markup
* libc/include/stdlib.h (arc4random): Declare if __BSD_VISIBLE.
(arc4random_buf): Likewise.
(arc4random_uniform): Likewise.
* libc/include/sys/unistd.h (getentropy): Likewise.
* libc/include/machine/_arc4random.h: New file.
* libc/stdlib/arc4random.c: Likewise.
* libc/stdlib/arc4random.h: Likewise.
* libc/stdlib/arc4random_uniform.c: Likewise.
* libc/stdlib/chacha_private.h: Likewise.
* libc/sys/rtems/include/machine/_arc4random.h: Likewise.
* libc/stdlib/Makefile.am (EXTENDED_SOURCES): Add arc4random.c
and arc4random_uniform.c.
* libc/stdlib/Makefile.in: Regenerate.
Jon Beniston