c2f5813ae0
sem_timedwait converts absolute timeouts to relative to pass them to the futex syscall. (Before the recent reimplementation, on x86_64 it used FUTEX_CLOCK_REALTIME, but not on other architectures.) Correctly implementing POSIX requirements, however, requires use of FUTEX_CLOCK_REALTIME; passing a relative timeout to the kernel does not conform to POSIX. The POSIX specification for sem_timedwait says "The timeout shall be based on the CLOCK_REALTIME clock.". The POSIX specification for clock_settime says "If the value of the CLOCK_REALTIME clock is set via clock_settime(), the new value of the clock shall be used to determine the time of expiration for absolute time services based upon the CLOCK_REALTIME clock. This applies to the time at which armed absolute timers expire. If the absolute time requested at the invocation of such a time service is before the new value of the clock, the time service shall expire immediately as if the clock had reached the requested time normally.". If a relative timeout is passed to the kernel, it is interpreted according to the CLOCK_MONOTONIC clock, and so fails to meet that POSIX requirement in the event of clock changes. This patch makes sem_timedwait use lll_futex_timed_wait_bitset with FUTEX_CLOCK_REALTIME when possible, as done in some other places in NPTL. FUTEX_CLOCK_REALTIME is always available for supported Linux kernel versions; unavailability of lll_futex_timed_wait_bitset is only an issue for hppa (an issue noted in <https://sourceware.org/glibc/wiki/PortStatus>, and fixed by the unreviewed <https://sourceware.org/ml/libc-alpha/2014-12/msg00655.html> that removes the hppa lowlevellock.h completely). In the FUTEX_CLOCK_REALTIME case, the glibc code still needs to check for negative tv_sec and handle that as timeout, because the Linux kernel returns EINVAL not ETIMEDOUT for that case, so resulting in failures of nptl/tst-abstime and nptl/tst-sem13 in the absence of that check. If we're trying to distinguish between Linux-specific and generic-futex NPTL code, I suppose having this in an nptl/ file isn't ideal, but there doesn't seem to be any better place at present. It's not possible to add a testcase for this issue to the testsuite because of the requirement to change the system clock as part of a test (this is a case where testing would require some form of container, with root in that container, and one whose CLOCK_REALTIME is isolated from that of the host; I'm not sure what forms of containers, short of a full virtual machine, provide that clock isolation). Tested for x86_64. Also tested for powerpc with the testcase included in the bug. [BZ #18138] * nptl/sem_waitcommon.c: Include <kernel-features.h>. (futex_abstimed_wait) [__ASSUME_FUTEX_CLOCK_REALTIME && lll_futex_timed_wait_bitset]: Use lll_futex_timed_wait_bitset with FUTEX_CLOCK_REALTIME instead of lll_futex_timed_wait.
This directory contains the sources of the GNU C Library. See the file "version.h" for what release version you have. The GNU C Library is the standard system C library for all GNU systems, and is an important part of what makes up a GNU system. It provides the system API for all programs written in C and C-compatible languages such as C++ and Objective C; the runtime facilities of other programming languages use the C library to access the underlying operating system. In GNU/Linux systems, the C library works with the Linux kernel to implement the operating system behavior seen by user applications. In GNU/Hurd systems, it works with a microkernel and Hurd servers. The GNU C Library implements much of the POSIX.1 functionality in the GNU/Hurd system, using configurations i[4567]86-*-gnu. The current GNU/Hurd support requires out-of-tree patches that will eventually be incorporated into an official GNU C Library release. When working with Linux kernels, this version of the GNU C Library requires Linux kernel version 2.6.32 or later. Also note that the shared version of the libgcc_s library must be installed for the pthread library to work correctly. The GNU C Library supports these configurations for using Linux kernels: aarch64*-*-linux-gnu alpha*-*-linux-gnu arm-*-linux-gnueabi hppa-*-linux-gnu Not currently functional without patches. i[4567]86-*-linux-gnu x86_64-*-linux-gnu Can build either x86_64 or x32 ia64-*-linux-gnu m68k-*-linux-gnu microblaze*-*-linux-gnu mips-*-linux-gnu mips64-*-linux-gnu powerpc-*-linux-gnu Hardware or software floating point, BE only. powerpc64*-*-linux-gnu Big-endian and little-endian. s390-*-linux-gnu s390x-*-linux-gnu sh[34]-*-linux-gnu sparc*-*-linux-gnu sparc64*-*-linux-gnu tilegx-*-linux-gnu tilepro-*-linux-gnu If you are interested in doing a port, please contact the glibc maintainers; see http://www.gnu.org/software/libc/ for more information. See the file INSTALL to find out how to configure, build, and install the GNU C Library. You might also consider reading the WWW pages for the C library at http://www.gnu.org/software/libc/. The GNU C Library is (almost) completely documented by the Texinfo manual found in the `manual/' subdirectory. The manual is still being updated and contains some known errors and omissions; we regret that we do not have the resources to work on the manual as much as we would like. For corrections to the manual, please file a bug in the `manual' component, following the bug-reporting instructions below. Please be sure to check the manual in the current development sources to see if your problem has already been corrected. Please see http://www.gnu.org/software/libc/bugs.html for bug reporting information. We are now using the Bugzilla system to track all bug reports. This web page gives detailed information on how to report bugs properly. The GNU C Library is free software. See the file COPYING.LIB for copying conditions, and LICENSES for notices about a few contributions that require these additional notices to be distributed. License copyright years may be listed using range notation, e.g., 1996-2015, indicating that every year in the range, inclusive, is a copyrightable year that would otherwise be listed individually.