| /* Optional code to distinguish library flavours. x86-64 version. |
| Copyright (C) 2015-2018 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 */ |