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glibc/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
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/* Optional code to distinguish library flavours. x86-64 version. | |
Copyright (C) 2015-2016 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 | |
<http://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 (memcmp (envline, "PREFER_MAP_32BIT_EXEC", 21) == 0) \ | |
GLRO(dl_x86_cpu_features).feature[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 */ |