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/* Optional code to distinguish library flavours. x86-64 version.
Copyright (C) 2015-2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#ifndef _DL_LIBRECON_H
#include <sysdeps/unix/sysv/linux/dl-librecon.h>
/* Recognizing extra environment variables. For 64-bit applications,
branch prediction performance may be negatively impacted when the
target of a branch is more than 4GB away from the branch. Add the
Prefer_MAP_32BIT_EXEC bit so that mmap will try to map executable
pages with MAP_32BIT first. NB: MAP_32BIT will map to lower 2GB,
not lower 4GB, address. Prefer_MAP_32BIT_EXEC reduces bits available
for address space layout randomization (ASLR). Prefer_MAP_32BIT_EXEC
is always disabled for SUID programs and can be enabled by setting
environment variable, LD_PREFER_MAP_32BIT_EXEC. */
#define EXTRA_LD_ENVVARS \
case 21: \
if (!__libc_enable_secure \
&& memcmp (envline, "PREFER_MAP_32BIT_EXEC", 21) == 0) \
GLRO(dl_x86_cpu_features).preferred[index_arch_Prefer_MAP_32BIT_EXEC] \
|= bit_arch_Prefer_MAP_32BIT_EXEC; \
break;
/* Extra unsecure variables. The names are all stuffed in a single
string which means they have to be terminated with a '\0' explicitly. */
#define EXTRA_UNSECURE_ENVVARS \
"LD_PREFER_MAP_32BIT_EXEC\0"
#endif /* dl-librecon.h */
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