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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>
43 lines
1.9 KiB
C
43 lines
1.9 KiB
C
/* Define INIT_ARCH so that midr is initialized before use by IFUNCs.
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This file is part of the GNU C Library.
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Copyright (C) 2017-2024 Free Software Foundation, Inc.
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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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#include <ldsodefs.h>
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#include <sys/auxv.h>
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/* Make glibc MTE-safe on a system that supports MTE in case user code
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enables tag checks independently of the mte_status of glibc. There
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is currently no ABI contract for enabling tag checks in user code,
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but this can be useful for debugging with MTE. */
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#define MTE_ENABLED() (GLRO(dl_hwcap2) & HWCAP2_MTE)
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#define INIT_ARCH() \
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uint64_t __attribute__((unused)) midr = \
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GLRO(dl_aarch64_cpu_features).midr_el1; \
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unsigned __attribute__((unused)) zva_size = \
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GLRO(dl_aarch64_cpu_features).zva_size; \
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bool __attribute__((unused)) bti = \
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HAVE_AARCH64_BTI && GLRO(dl_aarch64_cpu_features).bti; \
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bool __attribute__((unused)) mte = \
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MTE_ENABLED (); \
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bool __attribute__((unused)) sve = \
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GLRO(dl_aarch64_cpu_features).sve; \
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bool __attribute__((unused)) prefer_sve_ifuncs = \
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GLRO(dl_aarch64_cpu_features).prefer_sve_ifuncs; \
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bool __attribute__((unused)) mops = \
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GLRO(dl_aarch64_cpu_features).mops;
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