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In <https://sourceware.org/ml/libc-alpha/2013-05/msg00722.html> I remarked on the possibility of arithmetic in various nearbyint implementations being scheduled before feholdexcept calls, resulting in spurious "inexact" exceptions. I'm now actually observing this occurring in glibc built for ARM with GCC 7 (in fact, both copies of the same addition/subtraction sequence being combined and moved out before the conditionals and feholdexcept/fesetenv pairs), resulting in test failures. This patch makes the nearbyint implementations with this particular feholdexcept / arithmetic / fesetenv pattern consistently use math_opt_barrier on the function argument when first used in arithmetic, and also consistently use math_force_eval before fesetenv (the latter was generally already done, but the dbl-64/wordsize-64 implementation used math_opt_barrier instead, and as math_opt_barrier's intended effect is through its output value being used, such a use that doesn't use the return value is suspect). Tested for x86_64 (--disable-multi-arch so more of these implementations get used), and for ARM in a configuration where I saw the problem scheduling. [BZ #22225] * sysdeps/ieee754/dbl-64/s_nearbyint.c (__nearbyint): Use math_opt_barrier on argument when doing arithmetic on it. * sysdeps/ieee754/dbl-64/wordsize-64/s_nearbyint.c (__nearbyint): Likewise. Use math_force_eval not math_opt_barrier after arithmetic. * sysdeps/ieee754/flt-32/s_nearbyintf.c (__nearbyintf): Use math_opt_barrier on argument when doing arithmetic on it. * sysdeps/ieee754/ldbl-128/s_nearbyintl.c (__nearbyintl): Likewise. |
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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 3.2 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.