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commit b9eb92ab05204df772eb4929eccd018637c9f3e9
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Author: H.J. Lu <hjl.tools@gmail.com>
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Date: Wed Oct 21 14:44:23 2015 -0700
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Add Prefer_MAP_32BIT_EXEC to map executable pages with MAP_32BIT
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According to Silvermont software optimization guide, for 64-bit
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applications, branch prediction performance can be negatively impacted
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when the target of a branch is more than 4GB away from the branch. Add
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the Prefer_MAP_32BIT_EXEC bit so that mmap will try to map executable
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pages with MAP_32BIT first. NB: MAP_32BIT will map to lower 2GB, not
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lower 4GB, address. Prefer_MAP_32BIT_EXEC reduces bits available for
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address space layout randomization (ASLR), which is always disabled for
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SUID programs and can only be enabled by setting environment variable,
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LD_PREFER_MAP_32BIT_EXEC.
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On Fedora 23, this patch speeds up GCC 5 testsuite by 3% on Silvermont.
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[BZ #19367]
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* sysdeps/unix/sysv/linux/wordsize-64/mmap.c: New file.
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* sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h: Likewise.
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* sysdeps/unix/sysv/linux/x86_64/64/mmap.c: Likewise.
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* sysdeps/x86/cpu-features.h (bit_Prefer_MAP_32BIT_EXEC): New.
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(index_Prefer_MAP_32BIT_EXEC): Likewise.
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Index: glibc-2.17-c758a686/sysdeps/unix/sysv/linux/wordsize-64/mmap.c
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===================================================================
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--- /dev/null
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+++ glibc-2.17-c758a686/sysdeps/unix/sysv/linux/wordsize-64/mmap.c
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@@ -0,0 +1,40 @@
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+/* Linux mmap system call. 64-bit version.
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+ Copyright (C) 2015 Free Software Foundation, Inc.
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+
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+ This file is part of the GNU C Library.
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+
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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 License as
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+ published by the Free Software Foundation; either version 2.1 of the
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+ License, or (at your option) any later version.
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+
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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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+
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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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+ <http://www.gnu.org/licenses/>. */
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+
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+#include <sys/types.h>
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+#include <sys/mman.h>
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+#include <errno.h>
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+#include <sysdep.h>
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+
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+/* An architecture may override this. */
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+#ifndef MMAP_PREPARE
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+# define MMAP_PREPARE(addr, len, prot, flags, fd, offset)
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+#endif
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+
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+__ptr_t
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+__mmap (__ptr_t addr, size_t len, int prot, int flags, int fd, off_t offset)
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+{
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+ MMAP_PREPARE (addr, len, prot, flags, fd, offset);
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+ return (__ptr_t) INLINE_SYSCALL (mmap, 6, addr, len, prot, flags,
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+ fd, offset);
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+}
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+
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+weak_alias (__mmap, mmap)
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+weak_alias (__mmap, mmap64)
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+weak_alias (__mmap, __mmap64)
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Index: glibc-2.17-c758a686/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
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===================================================================
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--- /dev/null
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+++ glibc-2.17-c758a686/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
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@@ -0,0 +1,44 @@
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+/* Optional code to distinguish library flavours. x86-64 version.
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+ Copyright (C) 2015 Free Software Foundation, Inc.
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+ This file is part of the GNU C Library.
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+
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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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+
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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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+
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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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+ <http://www.gnu.org/licenses/>. */
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+
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+#ifndef _DL_LIBRECON_H
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+
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+#include <sysdeps/unix/sysv/linux/dl-librecon.h>
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+
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+/* Recognizing extra environment variables. For 64-bit applications,
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+ branch prediction performance may be negatively impacted when the
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+ target of a branch is more than 4GB away from the branch. Add the
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+ Prefer_MAP_32BIT_EXEC bit so that mmap will try to map executable
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+ pages with MAP_32BIT first. NB: MAP_32BIT will map to lower 2GB,
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+ not lower 4GB, address. Prefer_MAP_32BIT_EXEC reduces bits available
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+ for address space layout randomization (ASLR). Prefer_MAP_32BIT_EXEC
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+ is always disabled for SUID programs and can be enabled by setting
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+ environment variable, LD_PREFER_MAP_32BIT_EXEC. */
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+#define EXTRA_LD_ENVVARS \
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+ case 21: \
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+ if (memcmp (envline, "PREFER_MAP_32BIT_EXEC", 21) == 0) \
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+ GLRO(dl_x86_cpu_features).feature[index_Prefer_MAP_32BIT_EXEC] \
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+ = bit_Prefer_MAP_32BIT_EXEC; \
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+ break;
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+
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+/* Extra unsecure variables. The names are all stuffed in a single
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+ string which means they have to be terminated with a '\0' explicitly. */
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+#define EXTRA_UNSECURE_ENVVARS \
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+ "LD_PREFER_MAP_32BIT_EXEC\0"
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+
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+#endif /* dl-librecon.h */
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Index: glibc-2.17-c758a686/sysdeps/unix/sysv/linux/x86_64/64/mmap.c
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===================================================================
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--- /dev/null
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+++ glibc-2.17-c758a686/sysdeps/unix/sysv/linux/x86_64/64/mmap.c
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@@ -0,0 +1,37 @@
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+/* Linux mmap system call. x86-64 version.
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+ Copyright (C) 2015 Free Software Foundation, Inc.
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+
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+ This file is part of the GNU C Library.
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+
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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 License as
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+ published by the Free Software Foundation; either version 2.1 of the
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+ License, or (at your option) any later version.
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+
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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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+
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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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+ <http://www.gnu.org/licenses/>. */
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+
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+#include <ldsodefs.h>
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+
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+/* If the Prefer_MAP_32BIT_EXEC bit is set, try to map executable pages
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+ with MAP_32BIT first. */
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+#define MMAP_PREPARE(addr, len, prot, flags, fd, offset) \
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+ if ((addr) == NULL \
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+ && ((prot) & PROT_EXEC) != 0 \
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+ && HAS_ARCH_FEATURE (Prefer_MAP_32BIT_EXEC)) \
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+ { \
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+ __ptr_t ret = (__ptr_t) INLINE_SYSCALL (mmap, 6, (addr), (len), \
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+ (prot), \
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+ (flags) | MAP_32BIT, \
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+ (fd), (offset)); \
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+ if (ret != MAP_FAILED) \
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+ return ret; \
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+ }
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+
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+#include <sysdeps/unix/sysv/linux/wordsize-64/mmap.c>
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Index: glibc-2.17-c758a686/sysdeps/x86/cpu-features.h
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===================================================================
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--- glibc-2.17-c758a686.orig/sysdeps/x86/cpu-features.h
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+++ glibc-2.17-c758a686/sysdeps/x86/cpu-features.h
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@@ -32,6 +32,7 @@
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#define bit_AVX_Fast_Unaligned_Load (1 << 11)
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#define bit_AVX512F_Usable (1 << 12)
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#define bit_AVX512DQ_Usable (1 << 13)
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+#define bit_Prefer_MAP_32BIT_EXEC (1 << 16)
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/* CPUID Feature flags. */
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@@ -91,6 +92,7 @@
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# define index_AVX_Fast_Unaligned_Load FEATURE_INDEX_1*FEATURE_SIZE
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# define index_AVX512F_Usable FEATURE_INDEX_1*FEATURE_SIZE
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# define index_AVX512DQ_Usable FEATURE_INDEX_1*FEATURE_SIZE
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+# define index_Prefer_MAP_32BIT_EXEC FEATURE_INDEX_1*FEATURE_SIZE
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# if defined (_LIBC) && !IS_IN (nonlib)
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# ifdef __x86_64__
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@@ -267,6 +269,7 @@ extern const struct cpu_features *__get_
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# define index_AVX_Fast_Unaligned_Load FEATURE_INDEX_1
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# define index_AVX512F_Usable FEATURE_INDEX_1
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# define index_AVX512DQ_Usable FEATURE_INDEX_1
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+# define index_Prefer_MAP_32BIT_EXEC FEATURE_INDEX_1
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#endif /* !__ASSEMBLER__ */
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