The GNU C Library version 2.34 is now available

Carlos O'Donell
Mon Aug 2 03:53:38 GMT 2021

The GNU C Library

The GNU C Library version 2.34 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 2.34 release may be downloaded from:

The mirror list is at

NEWS for version 2.34

Major new features:

* In order to support smoother in-place-upgrades and to simplify
  the implementation of the runtime all functionality formerly
  implemented in the libraries libpthread, libdl, libutil, libanl has
  been integrated into libc.  New applications do not need to link with
  -lpthread, -ldl, -lutil, -lanl anymore.  For backwards compatibility,
  empty static archives libpthread.a, libdl.a, libutil.a, libanl.a are
  provided, so that the linker options keep working.  Applications which
  have been linked against glibc 2.33 or earlier continue to load the
  corresponding shared objects (which are now empty).  The integration
  of those libraries into libc means that additional symbols become
  available by default.  This can cause applications that contain weak
  references to take unexpected code paths that would only have been
  used in previous glibc versions when e.g. preloading,
  potentially exposing application bugs.

  PTHREAD_STACK_MIN is no longer constant and is redefined to
  sysconf(_SC_THREAD_STACK_MIN).  This supports dynamic sized register
  sets for modern architectural features like Arm SVE.

  or _GNU_SOURCE are defined, MINSIGSTKSZ and SIGSTKSZ are no longer
  constant on Linux.  MINSIGSTKSZ is redefined to sysconf(_SC_MINSIGSTKSZ)
  and SIGSTKSZ is redefined to sysconf (_SC_SIGSTKSZ).  This supports
  dynamic sized register sets for modern architectural features like
  Arm SVE.

* The dynamic linker implements the --list-diagnostics option, printing
  a dump of information related to IFUNC resolver operation and
  glibc-hwcaps subdirectory selection.

* On Linux, the function execveat has been added.  It operates similar to
  execve and it is is already used to implement fexecve without requiring
  /proc to be mounted.  However, different than fexecve, if the syscall is not
  supported by the kernel an error is returned instead of trying a fallback.

* The ISO C2X function timespec_getres has been added.

* The feature test macro __STDC_WANT_IEC_60559_EXT__, from draft ISO
  C2X, is supported to enable declarations of functions defined in Annex F
  of C2X.  Those declarations are also enabled when
  __STDC_WANT_IEC_60559_BFP_EXT__, as specified in TS 18661-1, is
  defined, and when _GNU_SOURCE is defined.

* On powerpc64*, glibc can now be compiled without scv support using the
  --disable-scv configure option.

* Add support for 64-bit time_t on configurations like x86 where time_t
  is traditionally 32-bit.  Although time_t still defaults to 32-bit on
  these configurations, this default may change in future versions.
  This is enabled with the _TIME_BITS preprocessor macro set to 64 and is
  only supported when LFS (_FILE_OFFSET_BITS=64) is also enabled.  It is
  only enabled for Linux and the full support requires a minimum kernel
  version of 5.1.

* The main gconv-modules file in glibc now contains only a small set of
  essential converter modules and the rest have been moved into a supplementary
  configuration file gconv-modules-extra.conf in the gconv-modules.d directory
  in the same GCONV_PATH.  Similarly, external converter modules directories
  may have supplementary configuration files in a gconv-modules.d directory
  with names ending with .conf to logically classify the converter modules in
  that directory.

* On Linux, a new tunable, glibc.pthread.stack_cache_size, can be used
  to configure the size of the thread stack cache.

* The function _Fork has been added as an async-signal-safe fork replacement
  since Austin Group issue 62 droped the async-signal-safe requirement for
  fork (and it will be included in the future POSIX standard).  The new _Fork
  function does not run any atfork function neither resets any internal state
  or lock (such as the malloc one), and only sets up a minimal state required
  to call async-signal-safe functions (such as raise or execve).  This function
  is currently a GNU extension.

* On Linux, the close_range function has been added.  It allows efficiently
  closing a range of file descriptors on recent kernels (version 5.9).

* The function closefrom has been added.  It closes all file descriptors
  greater than or equal to a given integer.  This function is a GNU extension,
  although it is also present in other systems.

* The posix_spawn_file_actions_addclosefrom_np function has been added,
  enabling posix_spawn and posix_spawnp to close all file descriptors greater
  than or equal to a given integer.  This function is a GNU extension,
  although Solaris also provides a similar function.

Deprecated and removed features, and other changes affecting compatibility:

* The function pthread_mutex_consistent_np has been deprecated; programs
  should use the equivalent standard function pthread_mutex_consistent

* The function pthread_mutexattr_getrobust_np has been deprecated;
  programs should use the equivalent standard function
  pthread_mutexattr_getrobust instead.

* The function pthread_mutexattr_setrobust_np has been deprecated;
  programs should use the equivalent standard function
  pthread_mutexattr_setrobust instead.

* The function pthread_yield has been deprecated; programs should use
  the equivalent standard function sched_yield instead.

* The function inet_neta declared in <arpa/inet.h> has been deprecated.

* Various rarely-used functions declared in <resolv.h> and
  <arpa/nameser.h> have been deprecated.  Applications are encouraged to
  use dedicated DNS processing libraries if applicable.  For <resolv.h>,
  this affects the functions dn_count_labels, fp_nquery, fp_query,
  fp_resstat, hostalias, loc_aton, loc_ntoa, p_cdname, p_cdnname,
  p_class, p_fqname, p_fqnname, p_option, p_query, p_rcode, p_time,
  p_type, putlong, putshort, res_hostalias, res_isourserver,
  res_nameinquery, res_queriesmatch, res_randomid, sym_ntop, sym_ntos,
  sym_ston.  For <arpa/nameser.h>, the functions ns_datetosecs,
  ns_format_ttl, ns_makecanon, ns_parse_ttl, ns_samedomain, ns_samename,
  ns_sprintrr, ns_sprintrrf, ns_subdomain have been deprecated.

* Various symbols previously defined in libresolv have been moved to libc
  in order to prepare for libresolv moving entirely into libc (see earlier
  entry for merging libraries into libc).  The symbols __dn_comp,
  __dn_expand, __dn_skipname, __res_dnok, __res_hnok, __res_mailok,
  __res_mkquery, __res_nmkquery, __res_nquery, __res_nquerydomain,
  __res_nsearch, __res_nsend, __res_ownok, __res_query, __res_querydomain,
  __res_search, __res_send formerly in libresolv have been renamed and no
  longer have a __ prefix.  They are now available in libc.

* The pthread cancellation handler is now installed with SA_RESTART and
  pthread_cancel will always send the internal SIGCANCEL on a cancellation
  request.  It should not be visible to applications since the cancellation
  handler should either act upon cancellation (if asynchronous cancellation
  is enabled) or ignore the cancellation internal signal.  However there are
  buggy kernel interfaces (for instance some CIFS versions) that could still
  see a spurious EINTR error when cancellation interrupts a blocking syscall.

* Previously, glibc installed its various shared objects under versioned
  file names such as  The ABI sonames (e.g.,
  were provided as symbolic links.  Starting with glibc 2.34, the shared
  objects are installed under their ABI sonames directly, without
  symbolic links.  This increases compatibility with distribution
  package managers that delete removed files late during the package
  upgrade or downgrade process.

* The symbols mallwatch and tr_break are now deprecated and no longer used in
  mtrace.  Similar functionality can be achieved by using conditional
  breakpoints within mtrace functions from within gdb.

* The __morecore and __after_morecore_hook malloc hooks and the default
  implementation __default_morecore have been removed from the API.  Existing
  applications will continue to link against these symbols but the interfaces
  no longer have any effect on malloc.

* Debugging features in malloc such as the MALLOC_CHECK_ environment variable
  (or the glibc.malloc.check tunable), mtrace() and mcheck() have now been
  disabled by default in the main C library.  Users looking to use these
  features now need to preload a new debugging DSO to get
  this functionality back.

* The deprecated functions malloc_get_state and malloc_set_state have been
  moved from the core C library into  Legacy applications
  that still use these functions will now need to preload
  in their environment using the LD_PRELOAD environment variable.

* The deprecated memory allocation hooks __malloc_hook, __realloc_hook,
  __memalign_hook and __free_hook are now removed from the API.  Compatibility
  symbols are present to support legacy programs but new applications can no
  longer link to these symbols.  These hooks no longer have any effect on glibc
  functionality.  The malloc debugging DSO currently
  supports hooks and can be preloaded to get this functionality back for older
  programs.  However this is a transitional measure and may be removed in a
  future release of the GNU C Library.  Users may port away from these hooks by
  writing and preloading their own malloc interposition library.

Changes to build and runtime requirements:

* On Linux, the shm_open, sem_open, and related functions now expect the
  file shared memory file system to be mounted at /dev/shm.  These functions
  no longer search among the system's mount points for a suitable
  replacement if /dev/shm is not available.

Security related changes:

  CVE-2021-27645: The nameserver caching daemon (nscd), when processing
  a request for netgroup lookup, may crash due to a double-free,
  potentially resulting in degraded service or Denial of Service on the
  local system.  Reported by Chris Schanzle.

  CVE-2021-33574: The mq_notify function has a potential use-after-free
  issue when using a notification type of SIGEV_THREAD and a thread
  attribute with a non-default affinity mask.

  CVE-2021-35942: The wordexp function may overflow the positional
  parameter number when processing the expansion resulting in a crash.
  Reported by Philippe Antoine.

The following bugs are resolved with this release:

  [4737] libc: fork is not async-signal-safe
  [5781] math: Slow dbl-64 sin/cos/sincos for special values
  [10353] libc: Methods for deleting all file descriptors greater than
    given integer (closefrom)
  [14185] glob: fnmatch() fails when '*' wildcard is applied on the file
    name containing multi-byte character(s)
  [14469] math: Inaccurate j0f function
  [14470] math: Inaccurate j1f function
  [14471] math: Inaccurate y0f function
  [14472] math: Inaccurate y1f function
  [14744] nptl: kill -32 $pid or kill -33 $pid on a process cancels a
    random thread
  [15271] dynamic-link: dlmopen()ed shared library with LM_ID_NEWLM
    crashes if it fails dlsym() twice
  [15648] nptl: multiple definition of `__lll_lock_wait_private'
  [16063] nptl: Provide a pthread_once variant in libc directly
  [17144] libc: syslog is not thread-safe if NO_SIGPIPE is not defined
  [17145] libc: syslog with LOG_CONS leaks console file descriptor
  [17183] manual: description of ENTRY struct in <search.h> in glibc
    manual is incorrect
  [18435] nptl: pthread_once hangs when init routine throws an exception
  [18524] nptl: Missing calloc error checking in
  [19329] dynamic-link: dl-tls.c assert failure at concurrent
    pthread_create and dlopen
  [19366] nptl: returning from a thread should disable cancellation
  [19511] nptl: 8MB memory leak in pthread_create in case of failure
    when non-root user changes priority
  [20802] dynamic-link: getauxval NULL pointer dereference after static
  [20813] nptl: pthread_exit is inconsistent between libc and libpthread
  [22057] malloc: malloc_usable_size is broken with mcheck
  [22668] locale: LC_COLLATE: the last character of ellipsis is not
    ordered correctly
  [23323] libc: [RFE] CSU startup hardening.
  [23328] malloc: Remove malloc hooks and ensure related APIs return no
  [23462] dynamic-link: Static binary with dynamic string tokens ($LIB,
    $PLATFORM, $ORIGIN) crashes
  [23489] libc: "gcc -lmcheck" aborts on free when using posix_memalign
  [23554] nptl: pthread_getattr_np reports wrong stack size with
  [24106] libc: Bash interpreter in ldd script is taken from host
  [24773] dynamic-link: dlerror in an secondary namespace does not use
    the right free implementation
  [25036] localedata: Update collation order for Swedish
  [25383] libc: where_is_shmfs/__shm_directory/SHM_GET_NAME may cause
    shm_open to pick wrong directory
  [25680] dynamic-link: ifuncmain9picstatic and ifuncmain9picstatic
    crash in IFUNC resolver due to stack canary (--enable-stack-
  [26874] build: -Warray-bounds in _IO_wdefault_doallocate
  [26983] math: [x86_64] x86_64 tgamma has too large ULP error
  [27111] dynamic-link: pthread_create and tls access use link_map
    objects that may be concurrently freed by dlclose
  [27132] malloc: memusagestat is linked to system librt, leading to
    undefined symbols on major version upgrade
  [27136] dynamic-link: dtv setup at thread creation may leave an entry
  [27249] libc: does not output signal number properly
  [27304] nptl: pthread_cond_destroy does not pass private flag to futex
    system calls
  [27318] dynamic-link: glibc fails to load binaries when built with
    -march=sandybridge:  CPU ISA level is lower than required
  [27343] nss: initgroups() SIGSEGVs when called on a system without
    nsswich.conf (in a chroot)
  [27346] dynamic-link: x86: PTWRITE feature check is missing
  [27389] network: NSS chroot hardening causes regressions in chroot
  [27403] dynamic-link: aarch64: tlsdesc htab is not freed on dlclose
  [27444] libc: sysconf reports unsupported option (-1) for
    _SC_LEVEL1_ICACHE_LINESIZE on X86 since v2.33
  [27462] nscd: double-free in nscd (CVE-2021-27645)
  [27468] malloc: aarch64: realloc crash with heap tagging: FAIL:
  [27498] dynamic-link: __dl_iterate_phdr lacks unwinding information
  [27511] libc: S390 memmove assumes Vector Facility when MIE Facility 3
    is present
  [27522] glob: glob, glob64 incorrectly marked as __THROW
  [27555] dynamic-link: Static tests fail with --enable-stack-
  [27559] libc: fstat(AT_FDCWD) succeeds (it shouldn't) and returns
    information for the current directory
  [27577] dynamic-link: elf/ --help doesn't work
  [27605] libc: tunables can't control xsave/xsavec selection in
  [27623] libc: powerpc: Missing registers in sc[v] clobbers list
  [27645] libc: [linux] sysconf(_SC_NPROCESSOR...) breaks down on
  [27646] dynamic-link: Linker error for non-existing NSS symbols (e.g.
    _nss_files_getcanonname_r) from within a dlmopen namespace.
  [27648] libc: FAIL: misc/tst-select
  [27650] stdio: vfscanf returns too early if a match is longer than
  [27651] libc: Performance regression after updating to 2.33
  [27655] string: Wrong size calculation in string/test-strnlen.c
  [27706] libc: select fails to update timeout on error
  [27709] libc: arm: FAIL: debug/tst-longjmp_chk2
  [27721] dynamic-link: x86: ld_audit ignores bind now for TLSDESC and
    tries resolving them lazily
  [27744] nptl: Support different libpthread/ load orders in
  [27749] libc: Data race __run_exit_handlers
  [27761] libc: getconf: Segmentation fault when passing '-vq' as
  [27832] nss: makedb.c:797:7: error: 'writev' specified size 4294967295
    exceeds maximum object size 2147483647
  [27870] malloc: MALLOC_CHECK_ causes realloc(valid_ptr, TOO_LARGE) to
    not set ENOMEM
  [27872] build: Obsolete configure option --enable-stackguard-
  [27873] build: tst-cpu-features-cpuinfo fail when building on AMD cpu
  [27882] localedata: Use U+00AF MACRON in more EBCDIC charsets
  [27892] libc: powerpc: scv ABI error handling fails to check
  [27896] nptl: mq_notify does not handle separately allocated thread
    attributes (CVE-2021-33574)
  [27901] libc: TEST_STACK_ALIGN doesn't work
  [27902] libc: The x86-64 clone wrapper fails to align child stack
  [27914] nptl: Install SIGSETXID handler with SA_ONSTACK
  [27939] libc: aarch64: clone does not align the stack
  [27968] libc: s390x: clone does not align the stack
  [28011] libc: Wild read in wordexp (parse_param) (CVE-2021-35942)
  [28024] string: s390(31bit): Wrong result of memchr (MEMCHR_Z900_G5)
    with n >= 0x80000000
  [28028] malloc: malloc: tcache shutdown sequence does not work if the
    thread never allocated anything
  [28033] libc: Need to check RTM_ALWAYS_ABORT for RTM
  [28064] string: x86_64:wcslen implementation list has wcsnlen
  [28067] libc: FAIL: posix/tst-spawn5
  [28068] malloc: FAIL: malloc/tst-mallocalign1-mcheck
  [28071] time: clock_gettime, gettimeofday, time lost vDSO acceleration
    on older kernels
  [28075] nis: Out-of-bounds static buffer read in nis_local_domain
  [28089] build: tst-tls20 fails when linker defaults to --as-needed
  [28090] build: elf/tst-cpu-features-cpuinfo-static fails on certain
    AMD64 cpus
  [28091] network: ns_name_skip may return 0 for domain names without

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
Alejandro Colomar \(man-pages\)
Alexandra Hájková
Alice Xu
Alyssa Ross
Andreas Roeseler
Andreas Schwab
Anton Blanchard
Arjun Shankar
Armin Brauns
Bruno Haible
Carlos O'Donell
Cooper Qu
DJ Delorie
Dan Raymond
Darius Rad
David Hughes
Fangrui Song
Florian Weimer
H.J. Lu
Hanataka Shinya
Hugo Gabriel Eyherabide
Jakub Jelinek
John David Anglin
Joseph Myers
Khem Raj
Lirong Yuan
Lucas A. M. Magalhaes
Lukasz Majewski
Maninder Singh
Mark Harris
Martin Sebor
Matheus Castanho
Michal Nazarewicz
Mike Hommey
Naohiro Tamura
Nicholas Piggin
Noah Goldstein
Paul Eggert
Paul Zimmermann
Pedro Franco de Carvalho
Raoni Fassina Firmino
Raphael Moreira Zinsly
Sajan Karumanchi
Samuel Thibault
Sebastian Rasmussen
Sergei Trofimovich
Shen-Ta Hsieh
Siddhesh Poyarekar
Stafford Horne
Stefan Liebler
Sunil K Pandey
Szabolcs Nagy
Tulio Magno Quites Machado Filho
Vineet Gupta
Vitaly Buka
Vitaly Chikunov
Wilco Dijkstra
Xiaoming Ni
Yang Xu
Érico Nogueira

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