2 min read

Last week, the GNU C Library version 2.30 was made available to all users. The major highlights of this release include new POSIX (Portable Operating System Interface)-proposed functions, support for Unicode 12.1.0, support to –preload argument to preload shared objects, addition of new functions such as getdents64, gettid, and tgkill to Linux and more.

The GNU C Library is used in the GNU systems, GNU/ Linux systems as well as on other systems that use Linux as the kernel. It is a portable and high performance C library.

Major new features in GNU C Library version 2.30

  • New POSIX-proposed pthread_cond_clockwait, pthread_mutex_clocklock, pthread_rwlock_clockrdlock, pthread_rwlock_clockwrlock and sem_clockwait functions have been introduced in GNU C Library version 2.30. All the functions allow waiting against CLOCK_MONOTONIC and CLOCK_REALTIME. 
  • The GNU C Library version 2.30 has an added support of Unicode 12.1.0. Character encoding, character type info, and transliteration tables have also been updated to Unicode 12.1.0.
  • The dynamic linker will now accept the –preload argument to preload shared objects along with the LD_PRELOAD environment variable.
  • The getdents64, gettid, and tgkill functions have been added on Linux.
  • Memory allocation functions malloc, calloc, realloc, reallocarray, valloc, pvalloc, memalign, and posix_memalign will need object size smaller than PTRDIFF_MAX. This will help the memory allocation functions to avoid potential undefined behavior with pointer subtraction within the allocated object, which caused ptrdiff_t type overflow.

Deprecated features influencing compatibility

  • Functions like clock_gettime, clock_getres, clock_settime, clock_getcpuclockid, clock_nanosleep have been removed from the librt library for new applications.
  • The outdated  XSI STREAMS header files and and the RES_INSECURE1 and RES_INSECURE2 option flags for the DNS stub have been abolished.
  • The support for “inet6” option in /etc/resolv.conf and the RES_USE_INET6 resolver flag have been eliminated.
  • The Linux-specific header and the sysctl function have been removed from the GNU C Library version 2.30 and also will not be present in the future versions of glibc. The getentropy function can be used for obtaining random bits.

Bug Fixes in GNU C Library version 2.30

  • gettid() to have a wrapper in libc
  • nftw() does not return dangling symlink’s inode in libc
  • mtrace hangs when MALLOC_TRACE is defined in malloc
  • memusagestat is built using system C library in malloc
  • libpthread IFUNC resolver for vfork can lead to crash in nptl

These are select few updates. For more information, you may go through the libc sourceware page.

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