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Old Linux kernels disable SVE after every system call. Calling the SVE-optimized memcpy afterwards will then cause a trap to reenable SVE. As a result, applications with a high use of syscalls may run slower with the SVE memcpy. This is true for kernels between 4.15.0 and before 6.2.0, except for 5.14.0 which was patched. Avoid this by checking the kernel version and selecting the SVE ifunc on modern kernels. Parse the kernel version reported by uname() into a 24-bit kernel.major.minor value without calling any library functions. If uname() is not supported or if the version format is not recognized, assume the kernel is modern. Tested-by: Florian Weimer <fweimer@redhat.com> Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
67 lines
2.2 KiB
C
67 lines
2.2 KiB
C
/* Multiple versions of memmove. AARCH64 version.
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Copyright (C) 2017-2024 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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/* Define multiple versions only for the definition in libc. */
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#if IS_IN (libc)
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/* Redefine memmove so that the compiler won't complain about the type
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mismatch with the IFUNC selector in strong_alias, below. */
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# undef memmove
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# define memmove __redirect_memmove
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# include <string.h>
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# include <init-arch.h>
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extern __typeof (__redirect_memmove) __libc_memmove;
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extern __typeof (__redirect_memmove) __memmove_generic attribute_hidden;
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extern __typeof (__redirect_memmove) __memmove_thunderx attribute_hidden;
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extern __typeof (__redirect_memmove) __memmove_thunderx2 attribute_hidden;
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extern __typeof (__redirect_memmove) __memmove_a64fx attribute_hidden;
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extern __typeof (__redirect_memmove) __memmove_sve attribute_hidden;
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extern __typeof (__redirect_memmove) __memmove_mops attribute_hidden;
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static inline __typeof (__redirect_memmove) *
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select_memmove_ifunc (void)
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{
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INIT_ARCH ();
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if (mops)
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return __memmove_mops;
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if (sve && HAVE_AARCH64_SVE_ASM)
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{
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if (IS_A64FX (midr))
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return __memmove_a64fx;
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return prefer_sve_ifuncs ? __memmove_sve : __memmove_generic;
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}
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if (IS_THUNDERX (midr))
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return __memmove_thunderx;
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if (IS_THUNDERX2 (midr) || IS_THUNDERX2PA (midr))
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return __memmove_thunderx2;
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return __memmove_generic;
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}
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libc_ifunc (__libc_memmove, select_memmove_ifunc ());
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# undef memmove
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strong_alias (__libc_memmove, memmove);
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#endif
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