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b9eb92ab | 1 | /* Optional code to distinguish library flavours. x86-64 version. |
2b778ceb | 2 | Copyright (C) 2015-2021 Free Software Foundation, Inc. |
b9eb92ab L |
3 | This file is part of the GNU C Library. |
4 | ||
5 | The GNU C Library is free software; you can redistribute it and/or | |
6 | modify it under the terms of the GNU Lesser General Public | |
7 | License as published by the Free Software Foundation; either | |
8 | version 2.1 of the License, or (at your option) any later version. | |
9 | ||
10 | The GNU C Library is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
13 | Lesser General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU Lesser General Public | |
16 | License along with the GNU C Library; if not, see | |
5a82c748 | 17 | <https://www.gnu.org/licenses/>. */ |
b9eb92ab L |
18 | |
19 | #ifndef _DL_LIBRECON_H | |
20 | ||
21 | #include <sysdeps/unix/sysv/linux/dl-librecon.h> | |
22 | ||
23 | /* Recognizing extra environment variables. For 64-bit applications, | |
24 | branch prediction performance may be negatively impacted when the | |
25 | target of a branch is more than 4GB away from the branch. Add the | |
26 | Prefer_MAP_32BIT_EXEC bit so that mmap will try to map executable | |
27 | pages with MAP_32BIT first. NB: MAP_32BIT will map to lower 2GB, | |
28 | not lower 4GB, address. Prefer_MAP_32BIT_EXEC reduces bits available | |
29 | for address space layout randomization (ASLR). Prefer_MAP_32BIT_EXEC | |
30 | is always disabled for SUID programs and can be enabled by setting | |
31 | environment variable, LD_PREFER_MAP_32BIT_EXEC. */ | |
32 | #define EXTRA_LD_ENVVARS \ | |
6aa3e97e | 33 | case 21: \ |
d5dfad43 MK |
34 | if (!__libc_enable_secure \ |
35 | && memcmp (envline, "PREFER_MAP_32BIT_EXEC", 21) == 0) \ | |
ecbbadbf | 36 | GLRO(dl_x86_cpu_features).preferred[index_arch_Prefer_MAP_32BIT_EXEC] \ |
6aa3e97e | 37 | |= bit_arch_Prefer_MAP_32BIT_EXEC; \ |
b9eb92ab L |
38 | break; |
39 | ||
40 | /* Extra unsecure variables. The names are all stuffed in a single | |
41 | string which means they have to be terminated with a '\0' explicitly. */ | |
42 | #define EXTRA_UNSECURE_ENVVARS \ | |
43 | "LD_PREFER_MAP_32BIT_EXEC\0" | |
44 | ||
45 | #endif /* dl-librecon.h */ |