NEWS for version 2.26
=====================

Major new features:

* A per-thread cache has been added to malloc. Access to the cache requires
  no locks and therefore significantly accelerates the fast path to allocate
  and free small amounts of memory. Refilling an empty cache requires
locking
  the underlying arena. Performance measurements show significant gains in a
  wide variety of user workloads. Workloads were captured using a special
  instrumented malloc and analyzed with a malloc simulator. Contributed by
  DJ Delorie with the help of Florian Weimer, and Carlos O'Donell.

* Unicode 10.0.0 Support: Character encoding, character type info, and
  transliteration tables are all updated to Unicode 10.0.0, using
  generator scripts contributed by Mike FABIAN (Red Hat).
  These updates cause user visible changes, especially the changes in
  wcwidth for many emoji characters cause problems when emoji sequences
  are rendered with pango, see for example:
  https://bugzilla.gnome.org/show_bug.cgi?id=780669#c5

* Collation of Hungarian has been overhauled and is now consistent with "The
  Rules of Hungarian Orthography, 12th edition" (Bug 18934).  Contributed by
  Egmont Koblinger.

* Improvements to the DNS stub resolver, contributed by Florian Weimer:

  - The GNU C Library will now detect when /etc/resolv.conf has been
    modified and reload the changed configuration.  The new resolver option
    “no-reload” (RES_NORELOAD) disables this behavior.

  - The GNU C Library now supports an arbitrary number of search domains
    (configured using the “search” directive in /etc/resolv.conf);
    previously, there was a hard limit of six domains.  For backward
    compatibility, applications that directly modify the ‘_res’ global
    object are still limited to six search domains.

  - When the “rotate” (RES_ROTATE) resolver option is active, the GNU C
    Library will now randomly pick a name server from the configuration as a
    starting point.  (Previously, the second name server was always used.)

* The tunables feature is now enabled by default.  This allows users to
tweak
  behavior of the GNU C Library using the GLIBC_TUNABLES environment
variable.

* New function reallocarray, which resizes an allocated block (like realloc)
  to the product of two sizes, with a guaranteed clean failure upon integer
  overflow in the multiplication.  Originally from OpenBSD, contributed by
  Dennis Wölfing and Rüdiger Sonderfeld.

* New wrappers for the Linux-specific system calls preadv2 and pwritev2.
  These are extended versions of preadv and pwritev, respectively, taking an
  additional flags argument.  The set of supported flags depends on the
  running kernel; full support currently requires kernel 4.7 or later.

* posix_spawnattr_setflags now supports the flag POSIX_SPAWN_SETSID, to
  create a new session ID for the spawned process.  This feature is
  scheduled to be added to the next major revision of POSIX; for the time
  being, it is available under _GNU_SOURCE.

* errno.h is now safe to use from C-preprocessed assembly language on all
  supported operating systems.  In this context, it will only define the
  Exxxx constants, as preprocessor macros expanding to integer literals.

* On ia64, powerpc64le, x86-32, and x86-64, the math library now implements
  128-bit floating point as defined by ISO/IEC/IEEE 60559:2011 (IEEE
  754-2008) and ISO/IEC TS 18661-3:2015.  Contributed by Paul E. Murphy,
  Gabriel F. T. Gomes, Tulio Magno Quites Machado Filho, and Joseph Myers.

  To compile programs that use this feature, the compiler must support
  128-bit floating point with the type name _Float128 (as defined by TS
  18661-3) or __float128 (the nonstandard name used by GCC for C++, and for
  C prior to version 7).  _GNU_SOURCE or __STDC_WANT_IEC_60559_TYPES_EXT__
  must be defined to make the new interfaces visible.

  The new functions and macros correspond to those present for other
  floating-point types (except for a few obsolescent interfaces not
  supported for the new type), with F128 or f128 suffixes; for example,
  strtof128, HUGE_VAL_F128 and cosf128.  Following TS 18661-3, there are no
  printf or scanf formats for the new type; the strfromf128 and strtof128
  interfaces should be used instead.

Deprecated and removed features, and other changes affecting compatibility:

* The synchronization that pthread_spin_unlock performs has been changed to
  now be equivalent to a C11 atomic store with release memory order to the
  spin lock's memory location.  Previously, several (but not all)
  architectures used stronger synchronization (e.g., containing what is
  often called a full barrier).  This change can improve performance, but
  may affect odd fringe uses of spin locks that depend on the previous
  behavior (e.g., using spin locks as atomic variables to try to implement
  Dekker's mutual exclusion algorithm).

* The port to Native Client running on ARMv7-A (--host=arm-nacl) has been
  removed.

* Sun RPC is deprecated.  The rpcgen program, librpcsvc, and Sun RPC headers
  will only be built and installed when the GNU C Library is configured with
  --enable-obsolete-rpc.  This allows alternative RPC implementations, such
  as TIRPC or rpcsvc-proto, to be used.

* The NIS(+) name service modules, libnss_nis, libnss_nisplus, and
  libnss_compat, are deprecated, and will not be built or installed by
  default.

  The NIS(+) support library, libnsl, is also deprecated.  By default, a
  compatibility shared library will be built and installed, but not headers
  or development libraries. Only a few NIS-related programs require this
  library.  (In particular, the GNU C Library has never required programs
  that use 'gethostbyname' to be linked with libnsl.)

  Replacement implementations based on TIRPC, which additionally support
  IPv6, are available from <https://github.com/thkukuk/>.  The configure
  option --enable-obsolete-nsl will cause libnsl's headers, and the NIS(+)
  name service modules, to be built and installed.

* The DNS stub resolver no longer performs EDNS fallback.  If EDNS or DNSSEC
  support is enabled, the configured recursive resolver must support EDNS.
  (Responding to EDNS-enabled queries with responses which are not
  EDNS-enabled is fine, but FORMERR responses are not.)

* res_mkquery and res_nmkquery no longer support the IQUERY opcode.  DNS
  servers have not supported this opcode for a long time.

* The _res_opcodes variable has been removed from libresolv.  It had been
  exported by accident.

* <string.h> no longer includes inline versions of any string functions,
  as this kind of optimization is better done by the compiler.  The macros
  __USE_STRING_INLINES and __NO_STRING_INLINES no longer have any effect.

* The nonstandard header <xlocale.h> has been removed.  Most programs should
  use <locale.h> instead.  If you have a specific need for the definition of
  locale_t with no other declarations, please contact
  libc-alpha@sourceware.org and explain.

* The obsolete header <sys/ultrasound.h> has been removed.

* The obsolete signal constant SIGUNUSED is no longer defined by <signal.h>.

* The obsolete function cfree has been removed.  Applications should use
  free instead.

* The stack_t type no longer has the name struct sigaltstack.  This changes
  the C++ name mangling for interfaces involving this type.

* The ucontext_t type no longer has the name struct ucontext.  This changes
  the C++ name mangling for interfaces involving this type.

* On M68k GNU/Linux and MIPS GNU/Linux, the fpregset_t type no longer has
  the name struct fpregset.  On Nios II GNU/Linux, the mcontext_t type no
  longer has the name struct mcontext.  On SPARC GNU/Linux, the struct
  mc_fq, struct rwindow, struct fpq and struct fq types are no longer
  defined in sys/ucontext.h, the mc_fpu_t type no longer has the name struct
  mc_fpu, the gwindows_t type no longer has the name struct gwindows and the
  fpregset_t type no longer has the name struct fpu.  This changes the C++
  name mangling for interfaces involving those types.

* On S/390 GNU/Linux, the constants defined by <sys/ptrace.h> have been
  synced with the kernel:

    - PTRACE_GETREGS, PTRACE_SETREGS, PTRACE_GETFPREGS and PTRACE_SETFPREGS
      are not supported on this architecture and have been removed.

    - PTRACE_SINGLEBLOCK, PTRACE_SECCOMP_GET_FILTER, PTRACE_PEEKUSR_AREA,
      PTRACE_POKEUSR_AREA, PTRACE_GET_LAST_BREAK, PTRACE_ENABLE_TE,
      PTRACE_DISABLE_TE and PTRACE_TE_ABORT_RAND have been added.

  Programs that assume the GET/SETREGS ptrace requests are universally
  available will now fail to build, instead of malfunctioning at runtime.

Changes to build and runtime requirements:

* Linux kernel 3.2 or later is required at runtime, on all architectures
  supported by that kernel.  (This is a change from version 2.25 only for
  x86-32 and x86-64.)

* GNU Binutils 2.25 or later is now required to build the GNU C Library.

* On most architectures, GCC 4.9 or later is required to build the GNU C
  Library.  On powerpc64le, GCC 6.2 or later is required.

  Older GCC versions and non-GNU compilers are still supported when
  compiling programs that use the GNU C Library.  (We do not know exactly
  how old, and some GNU extensions to C may be _de facto_ required.  If you
  are interested in helping us make this statement less vague, please
  contact libc-alpha@sourceware.org.)

Security related changes:

* The DNS stub resolver limits the advertised UDP buffer size to 1200 bytes,
  to avoid fragmentation-based spoofing attacks (CVE-2017-12132).

* LD_LIBRARY_PATH is now ignored in binaries running in privileged AT_SECURE
  mode to guard against local privilege escalation attacks
(CVE-2017-1000366).

* Avoid printing a backtrace from the __stack_chk_fail function since it is
  called on a corrupt stack and a backtrace is unreliable on a corrupt stack
  (CVE-2010-3192).

* A use-after-free vulnerability in clntudp_call in the Sun RPC system
has been
  fixed (CVE-2017-12133).

/lib64/ld-linux-x86-64.so.2 is the intepreter for dynamic
executables. Our /lib64 is a symlink to /lib.

Create the link /lib/ld-linux-x86-64.so.2 -> /lib/ld-X.XX.so

With glibc 2.26, the name service modules, libnss_nis, libnss_nisplus,
and libnss_compat, are deprecated, and will not be built or installed by
default.

We still require libnss_nis.so, because we use nis for
passwd and shadow in /etc/nsswitch.conf-

Add

    --enable-obsolete-nsl

to build and install the obsolete libnsl library and
depending NSS modules.

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
_Float128.

* 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,
pkey_get.

* 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",
respectively.

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
fix this.

* 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_switch_to_main_wget_area, _IO_switch_to_wget_mode,
_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
ignored.

* 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
programs.

* 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
instead.

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'
subdirectory.

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
script.)

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
of service.

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
Qualys.

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
current directory.

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.