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* The GNU C Library version 2.31 is now available
@ 2020-02-01 13:12 Siddhesh Poyarekar
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From: Siddhesh Poyarekar @ 2020-02-01 13:12 UTC (permalink / raw)
  To: libc-announce

The GNU C Library

The GNU C Library version 2.31 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.1-2017.  It is also
internationalized and has one of the most complete
internationalization interfaces known.

The GNU C Library webpage is at

Packages for the 2.31 release may be downloaded from:

The mirror list is at

NEWS for version 2.31

Major new features:

* The GNU C Library now supports a feature test macro _ISOC2X_SOURCE
  to enable features from the draft ISO C2X standard.  Only some
  features from this draft standard are supported by the GNU C
  Library, and as the draft is under active development, the set of
  features enabled by this macro is liable to change.  Features from
  C2X are also enabled by _GNU_SOURCE, or by compiling with "gcc

* The <math.h> functions that round their results to a narrower type
  now have corresponding type-generic macros in <tgmath.h>, as defined
  in TS 18661-1:2014 and TS 18661-3:2015 as amended by the resolution
  of Clarification Request 13 to TS 18661-3.

* The function pthread_clockjoin_np has been added, enabling join with
  a terminated thread with a specific clock.  It allows waiting
  against CLOCK_MONOTONIC and CLOCK_REALTIME.  This function is a GNU

* New locale added: mnw_MM (Mon language spoken in Myanmar).

* The DNS stub resolver will optionally send the AD (authenticated
  data) bit in queries if the trust-ad option is set via the options
  directive in /etc/resolv.conf (or if RES_TRUSTAD is set in
  _res.options).  In this mode, the AD bit, as provided by the name
  server, is available to applications which call res_search and
  related functions.  In the default mode, the AD bit is not set in
  queries, and it is automatically cleared in responses, indicating a
  lack of DNSSEC validation.  (Therefore, the name servers and the
  network path to them are treated as untrusted.)

Deprecated and removed features, and other changes affecting

* The totalorder and totalordermag functions, and the corresponding
  functions for other floating-point types, now take pointer arguments
  to avoid signaling NaNs possibly being converted to quiet NaNs in
  argument passing.  This is in accordance with the resolution of
  Clarification Request 25 to TS 18661-1, as applied for C2X.
  Existing binaries that pass floating-point arguments directly will
  continue to work.

* The obsolete function stime is no longer available to newly linked
  binaries, and its declaration has been removed from <time.h>.
  Programs that set the system time should use clock_settime instead.

* We plan to remove the obsolete function ftime, and the header
  <sys/timeb.h>, in a future version of glibc.  In this release, the
  header still exists but calling ftime will cause a compiler warning.
  All programs should use gettimeofday or clock_gettime instead.

* The gettimeofday function no longer reports information about a
  system-wide time zone.  This 4.2-BSD-era feature has been deprecated
  for many years, as it cannot handle the full complexity of the
  world's timezones, but hitherto we have supported it on a
  best-effort basis.  Changes required to support 64-bit time_t on
  32-bit architectures have made this no longer practical.

  As of this release, callers of gettimeofday with a non-null 'tzp'
  argument should expect to receive a 'struct timezone' whose
  tz_minuteswest and tz_dsttime fields are zero.  (For efficiency
  reasons, this does not always happen on a few Linux-based ports.
  This will be corrected in a future release.)

  All callers should supply a null pointer for the 'tzp' argument to
  gettimeofday.  For accurate information about the time zone
  associated with the current time, use the localtime function.

  gettimeofday itself is obsolescent according to POSIX.  We have no
  plans to remove access to this function, but portable programs
  should consider using clock_gettime instead.

* The settimeofday function can still be used to set a system-wide
  time zone when the operating system supports it.  This is because
  the Linux kernel reused the API, on some architectures, to describe
  a system-wide time-zone-like offset between the software clock
  maintained by the kernel, and the "RTC" clock that keeps time when
  the system is shut down.

  However, to reduce the odds of this offset being set by accident,
  settimeofday can no longer be used to set the time and the offset
  simultaneously.  If both of its two arguments are non-null, the call
  will fail (setting errno to EINVAL).

  Callers attempting to set this offset should also be prepared for
  the call to fail and set errno to ENOSYS; this already happens on
  the Hurd and on some Linux architectures.  The Linux kernel
  maintainers are discussing a more principled replacement for the
  reused API.  After a replacement becomes available, we will change
  settimeofday to fail with ENOSYS on all platforms when its 'tzp'
  argument is not a null pointer.

  settimeofday itself is obsolescent according to POSIX.  Programs
  that set the system time should use clock_settime and/or the adjtime
  family of functions instead.  We may cease to make settimeofday
  available to newly linked binaries after there is a replacement for
  Linux's time-zone-like offset API.

* SPARC ISA v7 is no longer supported.  v8 is still supported, but
  only if the optional CAS instruction is implemented (for instance,
  LEON processors are still supported, but SuperSPARC processors are

  As the oldest 64-bit SPARC ISA is v9, this only affects 32-bit

* If a lazy binding failure happens during dlopen, during the
  execution of an ELF constructor, the process is now terminated.
  Previously, the dynamic loader would return NULL from dlopen, with
  the lazy binding error captured in a dlerror message.  In general,
  this is unsafe because resetting the stack in an arbitrary function
  call is not possible.

* For MIPS hard-float ABIs, the GNU C Library will be configured to
  need an executable stack unless explicitly configured at build time
  to require minimum kernel version 4.8 or newer.  This is because
  executing floating-point branches on a non-executable stack on Linux
  kernels prior to 4.8 can lead to application crashes for some MIPS
  configurations. While currently PT_GNU_STACK is not widely used on
  MIPS, future releases of GCC are expected to enable non-executable
  stack by default with PT_GNU_STACK by default and is thus likely to
  trigger a crash on older kernels.

  The GNU C Library can be built with --enable-kernel=4.8.0 in order
  to keep a non-executable stack while dropping support for older

* System call wrappers for time system calls now use the new time64
  system calls when available. On 32-bit targets, these wrappers
  attempt to call the new system calls first and fall back to the
  older 32-bit time system calls if they are not present.  This may
  cause issues in environments that cannot handle unsupported system
  calls gracefully by returning -ENOSYS. Seccomp sandboxes are
  affected by this issue.

Changes to build and runtime requirements:

* It is no longer necessary to have recent Linux kernel headers to
  build working (non-stub) system call wrappers on all architectures
  except 64-bit RISC-V.  64-bit RISC-V requires a minimum kernel
  headers version of 5.0.

* The ChangeLog file is no longer present in the toplevel directory of
  the source tree.  ChangeLog files are located in the ChangeLog.old
  directory as ChangeLog.N where the highest N has the latest entries.

Security related changes:

  CVE-2019-19126: failed to ignore the LD_PREFER_MAP_32BIT_EXEC
  environment variable during program execution after a security
  transition, allowing local attackers to restrict the possible
  mapping addresses for loaded libraries and thus bypass ASLR for a
  setuid program.  Reported by Marcin Kościelnicki.

The following bugs are resolved with this release:

  [12031] localedata: iconv -t ascii//translit with Greek characters
  [15813] libc: Multiple issues in __gen_tempname
  [17726] libc: [arm, sparc] profil_counter should be compat symbol
  [18231] libc: ipc_perm struct's mode member has wrong type in
  [19767] libc: vdso is not used with static linking
  [19903] hurd: Shared mappings not being inherited by children
  [20358] network: RES_USE_DNSSEC sets DO; should also have a way to set
  [20839] dynamic-link: Incomplete rollback of dynamic linker state on
    linking failure
  [23132] localedata: Missing transliterations in Miscellaneous
    Mathematical Symbols-A/B Unicode blocks
  [23518] libc: Eliminate __libc_utmp_jump_table
  [24026] malloc: malloc_info() returns wrong numbers
  [24054] localedata: Many locales are missing date_fmt
  [24214] dynamic-link: user defined ifunc resolvers may run in ldd mode
  [24304] dynamic-link: Lazy binding failure during ELF
    constructors/destructors is not fatal
  [24376] libc: RISC-V symbol size confusion with _start
  [24682] localedata: zh_CN first weekday should be Monday per GB/T
  [24824] libc: test-in-container does not install charmap files
    compatible with localedef
  [24844] regex: regex bad pointer / leakage if malloc fails
  [24867] malloc: Unintended malloc_info formatting changes
  [24879] libc: login: utmp alarm timer can arrive after lock
  [24880] libc: login: utmp implementation uses struct flock with
  [24882] libc: login: pututline uses potentially outdated cache
  [24899] libc: Missing nonstring attributes in <utmp.h>, <utmpx.h>
  [24902] libc: login: Repeating pututxline on EINTR/EAGAIN causes stale
    utmp entries
  [24916] dynamic-link: [MIPS] Highest EI_ABIVERSION value not raised to
  [24930] dynamic-link: dlopen of PIE executable can result in
    _dl_allocate_tls_init assertion failure
  [24950] localedata: Top-of-tree glibc does not build with top-of-tree
    GCC (stringop-overflow error)
  [24959] time: librt IFUNC resolvers for clock_gettime and clock_*
    functions other  can lead to crashes
  [24967] libc: jemalloc static linking causes runtime failure
  [24986] libc: alpha: new getegid, geteuid and getppid syscalls used
  [25035] libc: sbrk() failure handled poorly in tunables_strdup
  [25087] dynamic-link: ldconfig mishandles unusual .dynstr placement
  [25097] libc: new -Warray-bounds with GCC 10
  [25112] dynamic-link: dlopen must not make new objects accessible when
    it still can fail with an error
  [25139] localedata: Please add the new mnw_MM locale
  [25149] regex: Array bounds violation in proceed_next_node
  [25157] dynamic-link: Audit cookie for the dynamic loader is not
    initialized correctly
  [25189] libc: glibc's __glibc_has_include causes issues with clang
  [25194] malloc: malloc.c: do_set_mxfast incorrectly casts the mallopt
    value to an unsigned
  [25204] dynamic-link: LD_PREFER_MAP_32BIT_EXEC not ignored in setuid
    binaries (CVE-2019-19126)
  [25225] libc: fails to link on x86 if GCC defaults to -fcf-
  [25226] string: strstr: Invalid result if needle crosses page on s390-
    z15 ifunc variant.
  [25232] string: <string.h> does not enable const correctness for
    strchr et al. for Clang++
  [25233] localedata: Consider "." as the thousands separator for sl_SI
  [25241] nptl: __SIZEOF_PTHREAD_MUTEX_T defined twice for x86
  [25251] build: Failure to run tests when CFLAGS contains -DNDEBUG.
  [25271] libc: undeclared identifier PTHREAD_MUTEX_DEFAULT when
    compiling with -std=c11
  [25323] localedata: km_KH: d_t_fmt contains "m" instead of "%M"
  [25324] localedata: lv_LV: d_t_fmt contains suspicious words in the
    time part
  [25396] dynamic-link: Failing dlopen can leave behind dangling GL
    (dl_initfirst) link map pointer
  [25401] malloc: pvalloc must not have __attribute_alloc_size__
  [25423] libc: Array overflow in backtrace on powerpc
  [25425] network: Missing call to __resolv_context_put in

Release Notes


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
Alexandra Hájková
Alistair Francis
Andreas Schwab
Andrew Eggenberger
Arjun Shankar
Aurelien Jarno
Carlos O'Donell
Chung-Lin Tang
DJ Delorie
Dmitry V. Levin
Dragan Mladjenovic
Egor Kobylkin
Emilio Cobos Álvarez
Emilio Pozuelo Monfort
Feng Xue
Florian Weimer
Gabriel F. T. Gomes
Gustavo Romero
H.J. Lu
Ian Kent
James Clarke
Jeremie Koenig
John David Anglin
Joseph Myers
Kamlesh Kumar
Krzysztof Koch
Leandro Pereira
Lucas A. M. Magalhaes
Lukasz Majewski
Marcin Kościelnicki
Matheus Castanho
Mihailo Stojanovic
Mike Crowe
Niklas Hambüchen
Paul A. Clarke
Paul Eggert
Petr Vorel
Rafal Luzynski
Rafał Lużyński
Rajalakshmi Srinivasaraghavan
Raoni Fassina Firmino
Richard Braun
Samuel Thibault
Sandra Loosemore
Siddhesh Poyarekar
Stefan Liebler
Svante Signell
Szabolcs Nagy
Talachan Mon
Thomas Schwinge
Tim Rühsen
Tulio Magno Quites Machado Filho
Wilco Dijkstra
Xuelei Zhang
Zack Weinberg

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