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The GNU C Library version 2.34 is now available
The GNU C Library version 2.34 is now available
Sun, 1 Aug 2021 23:52:49 -0400
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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 http://www.gnu.org/software/libc/
Packages for the X.Y release may be downloaded from:
The mirror list is at http://www.gnu.org/order/ftp.html
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 libpthread.so.0,
potentially exposing application bugs.
* When _DYNAMIC_STACK_SIZE_SOURCE or _GNU_SOURCE are defined,
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.
* Add _SC_MINSIGSTKSZ and _SC_SIGSTKSZ. When _DYNAMIC_STACK_SIZE_SOURCE
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
* 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
* 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
* The function pthread_mutexattr_setrobust_np has been deprecated;
programs should use the equivalent standard function
* 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 libc-2.33.so. The ABI sonames (e.g., libc.so.6)
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 libc_malloc_debug.so to get
this functionality back.
* The deprecated functions malloc_get_state and malloc_set_state have been
moved from the core C library into libc_malloc_debug.so. Legacy applications
that still use these functions will now need to preload libc_malloc_debug.so
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 libc_malloc_debug.so 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:
 libc: fork is not async-signal-safe
 math: Slow dbl-64 sin/cos/sincos for special values
 libc: Methods for deleting all file descriptors greater than
given integer (closefrom)
 glob: fnmatch() fails when '*' wildcard is applied on the file
name containing multi-byte character(s)
 math: Inaccurate j0f function
 math: Inaccurate j1f function
 math: Inaccurate y0f function
 math: Inaccurate y1f function
 nptl: kill -32 $pid or kill -33 $pid on a process cancels a
 dynamic-link: dlmopen()ed shared library with LM_ID_NEWLM
crashes if it fails dlsym() twice
 nptl: multiple definition of `__lll_lock_wait_private'
 nptl: Provide a pthread_once variant in libc directly
 libc: syslog is not thread-safe if NO_SIGPIPE is not defined
 libc: syslog with LOG_CONS leaks console file descriptor
 manual: description of ENTRY struct in <search.h> in glibc
manual is incorrect
 nptl: pthread_once hangs when init routine throws an exception
 nptl: Missing calloc error checking in
 dynamic-link: dl-tls.c assert failure at concurrent
pthread_create and dlopen
 nptl: returning from a thread should disable cancellation
 nptl: 8MB memory leak in pthread_create in case of failure
when non-root user changes priority
 dynamic-link: getauxval NULL pointer dereference after static
 nptl: pthread_exit is inconsistent between libc and libpthread
 malloc: malloc_usable_size is broken with mcheck
 locale: LC_COLLATE: the last character of ellipsis is not
 libc: [RFE] CSU startup hardening.
 malloc: Remove malloc hooks and ensure related APIs return no
 dynamic-link: Static binary with dynamic string tokens ($LIB,
$PLATFORM, $ORIGIN) crashes
 libc: "gcc -lmcheck" aborts on free when using posix_memalign
 nptl: pthread_getattr_np reports wrong stack size with
 libc: Bash interpreter in ldd script is taken from host
 dynamic-link: dlerror in an secondary namespace does not use
the right free implementation
 localedata: Update collation order for Swedish
 libc: where_is_shmfs/__shm_directory/SHM_GET_NAME may cause
shm_open to pick wrong directory
 dynamic-link: ifuncmain9picstatic and ifuncmain9picstatic
crash in IFUNC resolver due to stack canary (--enable-stack-
 build: -Warray-bounds in _IO_wdefault_doallocate
 math: [x86_64] x86_64 tgamma has too large ULP error
 dynamic-link: pthread_create and tls access use link_map
objects that may be concurrently freed by dlclose
 malloc: memusagestat is linked to system librt, leading to
undefined symbols on major version upgrade
 dynamic-link: dtv setup at thread creation may leave an entry
 libc: libSegFault.so does not output signal number properly
 nptl: pthread_cond_destroy does not pass private flag to futex
 dynamic-link: glibc fails to load binaries when built with
-march=sandybridge: CPU ISA level is lower than required
 nss: initgroups() SIGSEGVs when called on a system without
nsswich.conf (in a chroot)
 dynamic-link: x86: PTWRITE feature check is missing
 network: NSS chroot hardening causes regressions in chroot
 dynamic-link: aarch64: tlsdesc htab is not freed on dlclose
 libc: sysconf reports unsupported option (-1) for
_SC_LEVEL1_ICACHE_LINESIZE on X86 since v2.33
 nscd: double-free in nscd (CVE-2021-27645)
 malloc: aarch64: realloc crash with heap tagging: FAIL:
 dynamic-link: __dl_iterate_phdr lacks unwinding information
 libc: S390 memmove assumes Vector Facility when MIE Facility 3
 glob: glob, glob64 incorrectly marked as __THROW
 dynamic-link: Static tests fail with --enable-stack-
 libc: fstat(AT_FDCWD) succeeds (it shouldn't) and returns
information for the current directory
 dynamic-link: elf/ld.so --help doesn't work
 libc: tunables can't control xsave/xsavec selection in
 libc: powerpc: Missing registers in sc[v] clobbers list
 libc: [linux] sysconf(_SC_NPROCESSOR...) breaks down on
 dynamic-link: Linker error for non-existing NSS symbols (e.g.
_nss_files_getcanonname_r) from within a dlmopen namespace.
 libc: FAIL: misc/tst-select
 stdio: vfscanf returns too early if a match is longer than
 libc: Performance regression after updating to 2.33
 string: Wrong size calculation in string/test-strnlen.c
 libc: select fails to update timeout on error
 libc: arm: FAIL: debug/tst-longjmp_chk2
 dynamic-link: x86: ld_audit ignores bind now for TLSDESC and
tries resolving them lazily
 nptl: Support different libpthread/ld.so load orders in
 libc: Data race __run_exit_handlers
 libc: getconf: Segmentation fault when passing '-vq' as
 nss: makedb.c:797:7: error: 'writev' specified size 4294967295
exceeds maximum object size 2147483647
 malloc: MALLOC_CHECK_ causes realloc(valid_ptr, TOO_LARGE) to
not set ENOMEM
 build: Obsolete configure option --enable-stackguard-
 build: tst-cpu-features-cpuinfo fail when building on AMD cpu
 localedata: Use U+00AF MACRON in more EBCDIC charsets
 libc: powerpc: scv ABI error handling fails to check
 nptl: mq_notify does not handle separately allocated thread
 libc: TEST_STACK_ALIGN doesn't work
 libc: The x86-64 clone wrapper fails to align child stack
 nptl: Install SIGSETXID handler with SA_ONSTACK
 libc: aarch64: clone does not align the stack
 libc: s390x: clone does not align the stack
 libc: Wild read in wordexp (parse_param) (CVE-2021-35942)
 string: s390(31bit): Wrong result of memchr (MEMCHR_Z900_G5)
with n >= 0x80000000
 malloc: malloc: tcache shutdown sequence does not work if the
thread never allocated anything
 libc: Need to check RTM_ALWAYS_ABORT for RTM
 string: x86_64:wcslen implementation list has wcsnlen
 libc: FAIL: posix/tst-spawn5
 malloc: FAIL: malloc/tst-mallocalign1-mcheck
 time: clock_gettime, gettimeofday, time lost vDSO acceleration
on older kernels
 nis: Out-of-bounds static buffer read in nis_local_domain
 build: tst-tls20 fails when linker defaults to --as-needed
 build: elf/tst-cpu-features-cpuinfo-static fails on certain
 network: ns_name_skip may return 0 for domain names without
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:
Alejandro Colomar \(man-pages\)
Hugo Gabriel Eyherabide
John David Anglin
Lucas A. M. Magalhaes
Pedro Franco de Carvalho
Raoni Fassina Firmino
Raphael Moreira Zinsly
Sunil K Pandey
Tulio Magno Quites Machado Filho
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