The GNU C Library

The GNU C Library version 2.25 is now available.

The GNU C Library is used as *the* C library in the GNU system and
in GNU/Linux systems, as well as many other systems that use Linux
as the kernel.

The GNU C Library is primarily designed to be a portable
and high performance C library.  It follows all relevant
standards including ISO C11 and POSIX.1-2008.  It is also
internationalized and has one of the most complete
internationalization interfaces known.

The GNU C Library webpage is at

Packages for the 2.25 release may be downloaded from:

The mirror list is at

NEWS for version 2.25

* The feature test macro __STDC_WANT_LIB_EXT2__, from ISO/IEC TR
  24731-2:2010, is supported to enable declarations of functions from that
  TR.  Note that not all functions from that TR are supported by the GNU C

* The feature test macro __STDC_WANT_IEC_60559_BFP_EXT__, from ISO/IEC TS
  18661-1:2014, is supported to enable declarations of functions and macros
  from that TS.  Note that not all features from that TS are supported by
  the GNU C Library.

* The feature test macro __STDC_WANT_IEC_60559_FUNCS_EXT__, from ISO/IEC TS
  18661-4:2015, is supported to enable declarations of functions and macros
  from that TS.  Note that most features from that TS are not supported by
  the GNU C Library.

* The nonstandard feature selection macros _REENTRANT and _THREAD_SAFE are
  now treated as compatibility synonyms for _POSIX_C_SOURCE=199506L.
  Since the GNU C Library defaults to a much newer revision of POSIX, this
  will only affect programs that specifically request an old conformance
  mode.  For instance, a program compiled with -std=c89 -D_REENTRANT will
  see a change in the visible declarations, but a program compiled with
  just -D_REENTRANT, or -std=c99 -D_POSIX_C_SOURCE=200809L -D_REENTRANT,
  will not.

  Some C libraries once required _REENTRANT and/or _THREAD_SAFE to be
  defined by all multithreaded code, but glibc has not required this for
  many years.

* The inclusion of <sys/sysmacros.h> by <sys/types.h> is deprecated.  This
  means that in a future release, the macros “major”, “minor”, and “makedev”
  will only be available from <sys/sysmacros.h>.

  These macros are not part of POSIX nor XSI, and their names frequently
  collide with user code; see for instance glibc bug 19239 and Red Hat bug
  130601.  <stdlib.h> includes <sys/types.h> under _GNU_SOURCE, and C++ code
  presently cannot avoid being compiled under _GNU_SOURCE, exacerbating the

* New <fenv.h> features from TS 18661-1:2014 are added to libm: the
  fesetexcept, fetestexceptflag, fegetmode and fesetmode functions, the
  femode_t type and the FE_DFL_MODE and FE_SNANS_ALWAYS_SIGNAL macros.

* Integer width macros from TS 18661-1:2014 are added to <limits.h>:

* New <math.h> features are added from TS 18661-1:2014:

  - Signaling NaN macros: SNANF, SNAN, SNANL.

  - Nearest integer functions: roundeven, roundevenf, roundevenl, fromfp,
    fromfpf, fromfpl, ufromfp, ufromfpf, ufromfpl, fromfpx, fromfpxf,
    fromfpxl, ufromfpx, ufromfpxf, ufromfpxl.

  - llogb functions: the llogb, llogbf and llogbl functions, and the
    FP_LLOGB0 and FP_LLOGBNAN macros.

  - Max-min magnitude functions: fmaxmag, fmaxmagf, fmaxmagl, fminmag,
    fminmagf, fminmagl.

  - Comparison macros: iseqsig.

  - Classification macros: iscanonical, issubnormal, iszero.

  - Total order functions: totalorder, totalorderf, totalorderl,
    totalordermag, totalordermagf, totalordermagl.

  - Canonicalize functions: canonicalize, canonicalizef, canonicalizel.

  - NaN functions: getpayload, getpayloadf, getpayloadl, setpayload,
    setpayloadf, setpayloadl, setpayloadsig, setpayloadsigf, setpayloadsigl.

* The functions strfromd, strfromf, and strfroml, from ISO/IEC TS 18661-1:2014,
  are added to libc.  They convert a floating-point number into string.

* Most of glibc can now be built with the stack smashing protector enabled.
  It is recommended to build glibc with --enable-stack-protector=strong.
  Implemented by Nick Alcock (Oracle).

* The function explicit_bzero, from OpenBSD, has been added to libc.  It is
  intended to be used instead of memset() to erase sensitive data after use;
  the compiler will not optimize out calls to explicit_bzero even if they
  are "unnecessary" (in the sense that no _correct_ program can observe the
  effects of the memory clear).

* On ColdFire, MicroBlaze, Nios II and SH3, the float_t type is now defined
  to float instead of double.  This does not affect the ABI of any libraries
  that are part of the GNU C Library, but may affect the ABI of other
  libraries that use this type in their interfaces.

* On x86_64, when compiling with -mfpmath=387 or -mfpmath=sse+387, the
  float_t and double_t types are now defined to long double instead of float
  and double.  These options are not the default, and this does not affect
  the ABI of any libraries that are part of the GNU C Library, but it may
  affect the ABI of other libraries that use this type in their interfaces,
  if they are compiled or used with those options.

* The getentropy and getrandom functions, and the <sys/random.h> header file
  have been added.

* The buffer size for byte-oriented stdio streams is now limited to 8192
  bytes by default.  Previously, on Linux, the default buffer size on most
  file systems was 4096 bytes (and thus remains unchanged), except on
  network file systems, where the buffer size was unpredictable and could be
  as large as several megabytes.

* The <sys/quota.h> header now includes the <linux/quota.h> header.  Support
  for the Linux quota interface which predates kernel version 2.4.22 has
  been removed.

* The malloc_get_state and malloc_set_state functions have been removed.
  Already-existing binaries that dynamically link to these functions will
  get a hidden implementation in which malloc_get_state is a stub.  As far
  as we know, these functions are used only by GNU Emacs and this change
  will not adversely affect already-built Emacs executables.  Any undumped
  Emacs executables, which normally exist only during an Emacs build, should
  be rebuilt by re-running “./configure; make” in the Emacs build tree.

* The “ip6-dotint” and “no-ip6-dotint” resolver options, and the
  corresponding RES_NOIP6DOTINT flag from <resolv.h> have been removed.
  “no-ip6-dotint” had already been the default, and support for the
  “ip6-dotint” option was removed from the Internet in 2006.

* The "ip6-bytestring" resolver option and the corresponding RES_USEBSTRING
  flag from <resolv.h> have been removed.  The option relied on a
  backwards-incompatible DNS extension which was never deployed on the

  RES_BLAST defined in the <resolv.h> header file have been deprecated.
  They were already unimplemented.

* The "inet6" option in /etc/resolv.conf and the RES_USE_INET6 flag for
  _res.flags are deprecated.  The flag was standardized in RFC 2133, but
  removed again from the IETF name lookup interface specification in RFC
  2553.  Applications should use getaddrinfo instead.

* DNSSEC-related declarations and definitions have been removed from the
  <arpa/nameser.h> header file, and libresolv will no longer attempt to
  decode the data part of DNSSEC record types.  Previous versions of glibc
  only implemented minimal support for the previous version of DNSSEC, which
  is incompatible with the currently deployed version.

* The resource record type classification macros ns_t_qt_p, ns_t_mrr_p,
  ns_t_rr_p, ns_t_udp_p, ns_t_xfr_p have been removed from the
  <arpa/nameser.h> header file because the distinction between RR types and
  meta-RR types is not officially standardized, subject to revision, and
  thus not suitable for encoding in a macro.

* The types res_sendhookact, res_send_qhook, re_send_rhook, and the qhook
  and rhook members of the res_state type in <resolv.h> have been removed.
  The glibc stub resolver did not support these hooks, but the header file
  did not reflect that.

* For multi-arch support it is recommended to use a GCC which has
  been built with support for GNU indirect functions.  This ensures
  that correct debugging information is generated for functions
  selected by IFUNC resolvers.  This support can either be enabled by
  configuring GCC with '--enable-gnu-indirect-function', or by
  enabling it by default by setting 'default_gnu_indirect_function'
  variable for a particular architecture in the GCC source file

* GDB pretty printers have been added for mutex and condition variable
  structures in POSIX Threads. When installed and loaded in gdb these pretty
  printers show various pthread variables in human-readable form when read
  using the 'print' or 'display' commands in gdb.

* Tunables feature added to allow tweaking of the runtime for an application
  program.  This feature can be enabled with the '--enable-tunables' configure
  flag.  The GNU C Library manual has details on usage and README.tunables has
  instructions on adding new tunables to the library.

* A new version of condition variables functions have been implemented in
  the NPTL implementation of POSIX Threads to provide stronger ordering

* A new version of pthread_rwlock functions have been implemented to use a more
  scalable algorithm primarily through not using a critical section anymore to
  make state changes.

Security related changes:

* On ARM EABI (32-bit), generating a backtrace for execution contexts which
  have been created with makecontext could fail to terminate due to a
  missing .cantunwind annotation.  This has been observed to lead to a hang
  (denial of service) in some Go applications compiled with gccgo.  Reported
  by Andreas Schwab.  (CVE-2016-6323)

* The DNS stub resolver functions would crash due to a NULL pointer
  dereference when processing a query with a valid DNS question type which
  was used internally in the implementation.  The stub resolver now uses a
  question type which is outside the range of valid question type values.


This release was made possible by the contributions of many people.
The maintainers are grateful to everyone who has contributed
changes or bug reports.  These include:

Adhemerval Zanella
Alan Modra
Alexandre Oliva
Andreas Schwab
Andrew Senkevich
Aurelien Jarno
Brent W. Baccala
Carlos O'Donell
Chris Metcalf
Chung-Lin Tang
DJ Delorie
David S. Miller
Denis Kaganovich
Dmitry V. Levin
Ernestas Kulik
Florian Weimer
Gabriel F T Gomes
Gabriel F. T. Gomes
H.J. Lu
Jakub Jelinek
James Clarke
James Greenhalgh
Jim Meyering
John David Anglin
Joseph Myers
Maciej W. Rozycki
Mark Wielaard
Martin Galvan
Martin Pitt
Mike Frysinger
Märt Põder
Nick Alcock
Paul E. Murphy
Paul Murphy
Rajalakshmi Srinivasaraghavan
Rasmus Villemoes
Rical Jasan
Richard Henderson
Roland McGrath
Samuel Thibault
Siddhesh Poyarekar
Stefan Liebler
Steve Ellcey
Svante Signell
Szabolcs Nagy
Tom Tromey
Torvald Riegel
Tulio Magno Quites Machado Filho
Wilco Dijkstra
Yury Norov
Zack Weinberg

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