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The GNU C Library version 2.27 is now available
Dmitry V. Levin
The GNU C Library version 2.27 is now available
Fri, 2 Feb 2018 00:38:03 +0300
The GNU C Library
The GNU C Library version 2.27 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 https://www.gnu.org/software/libc/
Packages for the 2.27 release may be downloaded from:
The mirror list is at https://www.gnu.org/order/ftp.html
NEWS for version 2.27
Major new features:
* The GNU C Library can now be compiled with support for building static
PIE executables (See --enable-static-pie in INSTALL). These static PIE
executables are like static executables but can be loaded at any address
and provide additional security hardening benefits at the cost of some
memory and performance. When the library is built with --enable-static-pie
the resulting libc.a is usable with GCC 8 and above to create static PIE
executables using the GCC option '-static-pie'. This feature is currently
supported on i386, x86_64 and x32 with binutils 2.29 or later, and on
aarch64 with binutils 2.30 or later.
* Optimized x86-64 asin, atan2, exp, expf, log, pow, atan, sin, cosf,
sinf, sincosf and tan with FMA, contributed by Arjan van de Ven and
H.J. Lu from Intel.
* Optimized x86-64 trunc and truncf for processors with SSE4.1.
* Optimized generic expf, exp2f, logf, log2f, powf, sinf, cosf and sincosf.
* In order to support faster and safer process termination the malloc API
family of functions will no longer print a failure address and stack
backtrace after detecting heap corruption. The goal is to minimize the
amount of work done after corruption is detected and to avoid potential
security issues in continued process execution. Reducing shutdown time
leads to lower overall process restart latency, so there is benefit both
from a security and performance perspective.
* The abort function terminates the process immediately, without flushing
stdio streams. Previous glibc versions used to flush streams, resulting
in deadlocks and further data corruption. This change also affects
process aborts as the result of assertion failures.
* On platforms where long double has the IEEE binary128 format (aarch64,
alpha, mips64, riscv, s390 and sparc), the math library now implements
_Float128 interfaces for that type, as defined by ISO/IEC TS 18661-3:2015.
These are the same interfaces added in version 2.26 for some platforms where
this format is supported but is not the format of long double.
* On platforms with support for _Float64x (aarch64, alpha, i386, ia64,
mips64, powerpc64le, riscv, s390, sparc and x86_64), the math library now
implements interfaces for that type, as defined by ISO/IEC TS
18661-3:2015. These are corresponding interfaces to those supported for
* The math library now implements interfaces for the _Float32, _Float64 and
_Float32x types, as defined by ISO/IEC TS 18661-3:2015. These are
corresponding interfaces to those supported for _Float128.
* glibc now implements the memfd_create and mlock2 functions on Linux.
* Support for memory protection keys was added. The <sys/mman.h> header now
declares the functions pkey_alloc, pkey_free, pkey_mprotect, pkey_set,
* The copy_file_range function was added.
* Optimized memcpy, mempcpy, memmove, and memset for sparc M7.
* The ldconfig utility now processes `include' directives using the C/POSIX
collation ordering. Previous glibc versions used locale-specific
ordering, the change might break systems that relied on that.
* Support for two grammatical forms of month names has been added.
In a call to strftime, the "%B" and "%b" format specifiers will now
produce the grammatical form required when the month is used as part
of a complete date. New "%OB" and "%Ob" specifiers produce the form
required when the month is named by itself. For instance, in Greek
and in many Slavic and Baltic languages, "%B" will produce the month
in genitive case, and "%OB" will produce the month in nominative case.
In a call to strptime, "%B", "%b", "%h", "%OB", "%Ob", and "%Oh"
are all valid and will all accept any known form of month
name---standalone or complete, abbreviated or full. In a call to
nl_langinfo, the query constants MON_1..12 and ABMON_1..12 return
the strings used by "%B" and "%b", respectively. New query
constants ALTMON_1..12 and _NL_ABALTMON_1..12 return the strings
used by "%OB" and "%Ob", respectively.
In a locale definition file, use "alt_mon" and "ab_alt_mon" to
define the strings for %OB and %Ob, respectively; these have the
same syntax as "mon" and "abmon". These arrays are optional; if they
are not provided then they have the same content as "mon" and "abmon",
These features are provided for locales which define "alt_mon" and/or
"ab_alt_mon" in their locale source data. This release includes such
alternative month name data for the following languages: Belarusian,
Croatian, Greek, Lithuanian, Polish, Russian, and Ukrainian.
This feature is currently a GNU extension, but it is expected to
be added to the next revision of POSIX, and it is also already
available on some BSD-derived operating systems.
This feature will cause existing statically compiled applications
to fail to load locales and fall back to the builtin C/POSIX locales.
See notes below for other changes affecting compatibility.
* Support for the RISC-V ISA running on Linux has been added. This port
requires at least binutils-2.30, gcc-7.3.0, and linux-4.15; and is supported
for the following ISA and ABI pairs:
- rv64imac lp64
- rv64imafdc lp64
- rv64imafdc lp64d
Deprecated and removed features, and other changes affecting compatibility:
* Statically compiled applications attempting to load locales compiled for the
GNU C Library version 2.27 will fail and fall back to the builtin C/POSIX
locale. The reason for this is that the addition of the new "%OB" and "%Ob",
support for two grammatical forms of the month names, also extends the locale
data binary format. Static applications needing locale support must be
recompiled to match the runtime and data they are deployed with. In some
distributions there is an upgrade window where dynamically linked applications
may use a new library but the old locale data and also fall back to the
builtin C/POSIX locales; restarting the application process is sufficient to
* Support for statically linked applications which call dlopen is deprecated
and will be removed in a future version of glibc. Applications which call
dlopen need to be linked dynamically instead.
* Support for old programs which use internal stdio data structures and
functions is deprecated. This includes programs which use the C++ streams
provided by libstdc++ in GCC 2.95. Programs which use the internal
symbols _IO_adjust_wcolumn, _IO_default_doallocate, _IO_default_finish,
_IO_default_pbackfail, _IO_default_uflow, _IO_default_xsgetn,
_IO_default_xsputn, _IO_doallocbuf, _IO_do_write, _IO_file_attach,
_IO_file_close, _IO_file_close_it, _IO_file_doallocate, _IO_file_fopen,
_IO_file_init, _IO_file_jumps, _IO_fileno, _IO_file_open,
_IO_file_overflow, _IO_file_read, _IO_file_seek, _IO_file_seekoff,
_IO_file_setbuf, _IO_file_stat, _IO_file_sync, _IO_file_underflow,
_IO_file_write, _IO_file_xsputn, _IO_flockfile, _IO_flush_all,
_IO_flush_all_linebuffered, _IO_free_backup_area, _IO_free_wbackup_area,
_IO_init, _IO_init_marker, _IO_init_wmarker, _IO_iter_begin, _IO_iter_end,
_IO_iter_file, _IO_iter_next, _IO_least_wmarker, _IO_link_in,
_IO_list_all, _IO_list_lock, _IO_list_resetlock, _IO_list_unlock,
_IO_marker_delta, _IO_marker_difference, _IO_remove_marker, _IO_seekmark,
_IO_seekwmark, _IO_str_init_readonly, _IO_str_init_static,
_IO_str_overflow, _IO_str_pbackfail, _IO_str_seekoff, _IO_str_underflow,
_IO_unsave_wmarkers, _IO_wdefault_doallocate, _IO_wdefault_finish,
_IO_wdefault_pbackfail, _IO_wdefault_setbuf, _IO_wdefault_uflow,
_IO_wdefault_xsgetn, _IO_wdefault_xsputn, _IO_wdoallocbuf, _IO_wdo_write,
_IO_wfile_jumps, _IO_wfile_overflow, _IO_wfile_sync, _IO_wfile_underflow,
_IO_wfile_xsputn, _IO_wmarker_delta, or _IO_wsetb may stop working with a
future version of glibc. Unlike other symbol removals, these old
applications will not be supported using compatibility symbols.
* On GNU/Linux, the obsolete Linux constant PTRACE_SEIZE_DEVEL is no longer
defined by <sys/ptrace.h>.
* libm no longer supports SVID error handling (calling a user-provided
matherr function on error) or the _LIB_VERSION variable to control error
handling. (SVID error handling and the _LIB_VERSION variable still work
for binaries linked against older versions of the GNU C Library.) The
libieee.a library is no longer provided. math.h no longer defines struct
exception, or the macros X_TLOSS, DOMAIN, SING, OVERFLOW, UNDERFLOW,
TLOSS, PLOSS and HUGE.
* The libm functions pow10, pow10f and pow10l are no longer supported for
new programs. Programs should use the standard names exp10, exp10f and
exp10l for these functions instead.
* The mcontext_t type is no longer the same as struct sigcontext. On
platforms where it was previously the same, this changes the C++ name
mangling for interfaces involving this type.
* The add-ons mechanism for building additional packages at the same time as
glibc has been removed. The --enable-add-ons configure option is now
* The --without-fp configure option is now ignored. Whether hardware
floating-point instructions are used is now configured based on whether
the compiler used at configure time (without any options implied by a
--with-cpu= configure option) uses such instructions.
* The res_hnok, res_dnok, res_mailok and res_ownok functions now check that
the specified string can be parsed as a domain name.
* In the malloc_info output, the <heap> element may contain another <aspace>
element, "subheaps", which contains the number of sub-heaps.
* The libresolv function p_secstodate is no longer supported for new
* The tilepro-*-linux-gnu configuration is no longer supported.
* The nonstandard header files <libio.h> and <_G_config.h> are deprecated
and will be removed in a future release. Software that is still using
either header should be updated to use standard <stdio.h> interfaces
libio.h was originally the header for a set of supported GNU extensions,
but they have not been maintained as such in many years, they are now
standing in the way of improvements to stdio, and we don't think there are
any remaining external users. _G_config.h was never intended for public
use, but predates the bits convention.
Changes to build and runtime requirements:
* bison version 2.7 or later is required to generate code in the 'intl'
Security related changes:
CVE-2009-5064: The ldd script would sometimes run the program under
examination directly, without preventing code execution through the
dynamic linker. (The glibc project disputes that this is a security
vulnerability; only trusted binaries must be examined using the ldd
CVE-2017-15670: The glob function, when invoked with GLOB_TILDE,
suffered from a one-byte overflow during ~ operator processing (either
on the stack or the heap, depending on the length of the user name).
Reported by Tim Rühsen.
CVE-2017-15671: The glob function, when invoked with GLOB_TILDE,
would sometimes fail to free memory allocated during ~ operator
processing, leading to a memory leak and, potentially, to a denial
CVE-2017-15804: The glob function, when invoked with GLOB_TILDE and
without GLOB_NOESCAPE, could write past the end of a buffer while
unescaping user names. Reported by Tim Rühsen.
CVE-2017-17426: The malloc function, when called with an object size near
the value SIZE_MAX, would return a pointer to a buffer which is too small,
instead of NULL. This was a regression introduced with the new malloc
thread cache in glibc 2.26. Reported by Iain Buclaw.
CVE-2017-1000408: Incorrect array size computation in _dl_init_paths leads
to the allocation of too much memory. (This is not a security bug per se,
it is mentioned here only because of the CVE assignment.) Reported by
CVE-2017-1000409: Buffer overflow in _dl_init_paths due to miscomputation
of the number of search path components. (This is not a security
vulnerability per se because no trust boundary is crossed if the fix for
CVE-2017-1000366 has been applied, but it is mentioned here only because
of the CVE assignment.) Reported by Qualys.
CVE-2017-16997: Incorrect handling of RPATH or RUNPATH containing $ORIGIN
for AT_SECURE or SUID binaries could be used to load libraries from the
CVE-2018-1000001: Buffer underflow in realpath function when getcwd function
succeeds without returning an absolute path due to unexpected behaviour
of the Linux kernel getcwd syscall. Reported by halfdog.
CVE-2018-6485: The posix_memalign and memalign functions, when called with
an object size near the value of SIZE_MAX, would return a pointer to a
buffer which is too small, instead of NULL. Reported by Jakub Wilk.
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:
David S. Miller
Dmitry V. Levin
Dragan Stanojević - Nevidljivi
Gabriel F. T. Gomes
John David Anglin
Jose E. Marchesi
Julen Ruiz Aizpuru
Tulio Magno Quites Machado Filho
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