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On 32-bit x86 with -mfpmath=sse, and on x86_64 with --disable-multi-arch, the tests of ffma and its aliases (fma narrowing from binary64 to binary32) fail. This is probably the issue reported by H.J. in <https://sourceware.org/pipermail/libc-alpha/2021-September/131277.html>. The problem is the use of fenv_private.h macros in the round-to-odd implementation. Those macros are set up to manipulate only one of the SSE and 387 floating-point state, whichever is relevant for the type indicated by the suffix on the macro name. But x86 configurations sometimes use the ldbl-96 implementation of binary64 fma (that's where --disable-multi-arch is relevant for x86_64: it causes the ldbl-96 implementation to be used, instead of an IFUNC implementation that falls back to the dbl-64 version), contrary to the expectations of those macros for functions operating on double when __SSE2_MATH__ is defined. This can be addressed by using the default versions of those macros (giving x86 its own version of s_ffma.c), as is done for the *f128 macro variants where it depends on the details of how GCC was configured when building libgcc which floating-point state is affected by _Float128 arithmetic. The issue only applies when __SSE2_MATH__ is defined, and doesn't apply when __FP_FAST_FMA is defined (because in that case, fma will be inlined by the compiler, meaning it's definitely an SSE operation; for the same reason, this is not an issue for narrowing sqrt, as hardware sqrt is always inlined in that implementation for x86), but in other cases it's safest to use the default versions of the fenv_private.h macros to ensure things work whichever fma implementation is used. Tested for x86_64 (with and without --disable-multi-arch) and x86 (with and without -mfpmath=sse). |
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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. 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 arc*-*-linux-gnu arm-*-linux-gnueabi csky-*-linux-gnuabiv2 hppa-*-linux-gnu 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 riscv32-*-linux-gnu riscv64-*-linux-gnu sh[34]-*-linux-gnu sparc*-*-linux-gnu sparc64*-*-linux-gnu If you are interested in doing a port, please contact the glibc maintainers; see https://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 https://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 https://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.