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On AVX machines with XGETBV (ECX == 1) like Skylake processors, (gdb) disass _dl_runtime_resolve_avx_opt Dump of assembler code for function _dl_runtime_resolve_avx_opt: 0x0000000000015890 <+0>: push %rax 0x0000000000015891 <+1>: push %rcx 0x0000000000015892 <+2>: push %rdx 0x0000000000015893 <+3>: mov $0x1,%ecx 0x0000000000015898 <+8>: xgetbv 0x000000000001589b <+11>: mov %eax,%r11d 0x000000000001589e <+14>: pop %rdx 0x000000000001589f <+15>: pop %rcx 0x00000000000158a0 <+16>: pop %rax 0x00000000000158a1 <+17>: and $0x4,%r11d 0x00000000000158a5 <+21>: bnd je 0x16200 <_dl_runtime_resolve_sse_vex> End of assembler dump. is slower than: (gdb) disass _dl_runtime_resolve_avx_slow Dump of assembler code for function _dl_runtime_resolve_avx_slow: 0x0000000000015850 <+0>: vorpd %ymm0,%ymm1,%ymm8 0x0000000000015854 <+4>: vorpd %ymm2,%ymm3,%ymm9 0x0000000000015858 <+8>: vorpd %ymm4,%ymm5,%ymm10 0x000000000001585c <+12>: vorpd %ymm6,%ymm7,%ymm11 0x0000000000015860 <+16>: vorpd %ymm8,%ymm9,%ymm9 0x0000000000015865 <+21>: vorpd %ymm10,%ymm11,%ymm10 0x000000000001586a <+26>: vpcmpeqd %xmm8,%xmm8,%xmm8 0x000000000001586f <+31>: vorpd %ymm9,%ymm10,%ymm10 0x0000000000015874 <+36>: vptest %ymm10,%ymm8 0x0000000000015879 <+41>: bnd jae 0x158b0 <_dl_runtime_resolve_avx> 0x000000000001587c <+44>: vzeroupper 0x000000000001587f <+47>: bnd jmpq 0x16200 <_dl_runtime_resolve_sse_vex> End of assembler dump. (gdb) since xgetbv takes much more cycles than single cycle operations like vpord/vvpcmpeq/ptest. _dl_runtime_resolve_opt should be used only with AVX512 where AVX512 instructions lead to lower CPU frequency on Skylake server. [BZ #21871] * sysdeps/x86/cpu-features.c (init_cpu_features): Set bit_arch_Use_dl_runtime_resolve_opt only with AVX512F.
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.