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 http://www.gnu.org/software/libc/

Packages for the 2.31 release may be downloaded from:
        http://ftpmirror.gnu.org/libc/
        http://ftp.gnu.org/gnu/libc/

The mirror list is at http://www.gnu.org/order/ftp.html

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 -std=gnu2x".

* 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 extension.

* 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 compatibility:

* 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 not).

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

* 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 kernels.

* 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: ld.so 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 sys/ipc.h
  [19767] libc: vdso is not used with static linking
  [19903] hurd: Shared mappings not being inherited by children processes
  [20358] network: RES_USE_DNSSEC sets DO; should also have a way to set AD
  [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
    7408-2005
  [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 acquisition
  [24880] libc: login: utmp implementation uses struct flock with fcntl64
  [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
    ABSOLUTE ABI
  [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
    unconditionally
  [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
    -frewrite-includes
  [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: ld.so fails to link on x86 if GCC defaults to -fcf-
    protection
  [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
    (Slovenian)
  [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
    getaddrinfo.c:gethosts

Release Notes
=============

https://sourceware.org/glibc/wiki/Release/2.31

Contributors
============

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
Mike FABIAN
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
liqingqing
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