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x86: Set FSGSBASE to active if enabled by kernel
Linux kernel uses AT_HWCAP2 to indicate if FSGSBASE instructions are enabled. If the HWCAP2_FSGSBASE bit in AT_HWCAP2 is set, FSGSBASE instructions can be used in user space. Define dl_check_hwcap2 to set the FSGSBASE feature to active on Linux when the HWCAP2_FSGSBASE bit is set. Add a test to verify that FSGSBASE is active on current kernels. NB: This test will fail if the kernel doesn't set the HWCAP2_FSGSBASE bit in AT_HWCAP2 while fsgsbase shows up in /proc/cpuinfo. Reviewed-by: Florian Weimer <fweimer@redhat.com>
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27
sysdeps/unix/sysv/linux/x86/dl-hwcap2.h
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27
sysdeps/unix/sysv/linux/x86/dl-hwcap2.h
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@ -0,0 +1,27 @@
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/* Handle AT_HWCAP2. Linux/x86 version.
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Copyright (C) 2023 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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/* The following must match the kernel's <asm/hwcap2.h>. */
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#define HWCAP2_RING3MWAIT (1 << 0)
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#define HWCAP2_FSGSBASE (1 << 1)
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static inline void
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dl_check_hwcap2 (struct cpu_features *cpu_features)
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{
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if ((GLRO(dl_hwcap2) & HWCAP2_FSGSBASE) != 0)
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CPU_FEATURE_SET_ACTIVE (cpu_features, FSGSBASE);
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}
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@ -22,6 +22,7 @@
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#include <cacheinfo.h>
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#include <dl-cacheinfo.h>
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#include <dl-minsigstacksize.h>
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#include <dl-hwcap2.h>
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extern void TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *)
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attribute_hidden;
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@ -299,6 +300,8 @@ update_active (struct cpu_features *cpu_features)
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CPU_FEATURE_SET_ACTIVE (cpu_features, WIDE_KL);
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}
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dl_check_hwcap2 (cpu_features);
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cpu_features->isa_1 = get_isa_level (cpu_features);
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}
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21
sysdeps/x86/dl-hwcap2.h
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21
sysdeps/x86/dl-hwcap2.h
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/* Handle AT_HWCAP2. Generic x86 version.
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Copyright (C) 2023 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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static inline void
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dl_check_hwcap2 (struct cpu_features *cpu_features)
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{
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}
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@ -96,6 +96,11 @@ check_proc (const char *proc_name, const char *search_name, int flag,
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CPU_FEATURE_USABLE (name), \
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"HAS_CPU_FEATURE (" #name ")")
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#define CHECK_PROC_ACTIVE(str, name) \
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check_proc (#str, " "#str" ", CPU_FEATURE_USABLE (name), \
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CPU_FEATURE_USABLE (name), \
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"CPU_FEATURE_USABLE (" #name ")")
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static int
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do_test (int argc, char **argv)
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{
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@ -298,6 +303,8 @@ do_test (int argc, char **argv)
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fails += CHECK_PROC (xsaves, XSAVES);
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fails += CHECK_PROC (xtpr, XTPRUPDCTRL);
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fails += CHECK_PROC_ACTIVE (fsgsbase, FSGSBASE);
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printf ("%d differences between /proc/cpuinfo and glibc code.\n", fails);
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return (fails != 0);
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