C

New built-in functions:

New command-line options:

Inter-procedural optimization improvements:

Link-time optimization improvements:

Profile driven optimization improvements:

Version 2.6 of the OpenACC specification is now supported in the C, C++ and Fortran compilers. See the implementation status section on the OpenACC wiki page and the run-time library documentation for further information.

OpenMP and OpenACC now support offloading to AMD Radeon (GCN) GPUs; supported are the third-generation Fiji (fiji) and the fifth-generation VEGA 10/VEGA 20 (gfx900 or gfx906).

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.)

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.

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.

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).

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.

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.

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.