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a945c346 | 1 | /* Copyright (C) 2012-2024 Free Software Foundation, Inc. |
2077db1b CT |
2 | |
3 | This file is part of GCC. | |
4 | ||
5 | GCC is free software; you can redistribute it and/or modify it under | |
6 | the terms of the GNU General Public License as published by the Free | |
7 | Software Foundation; either version 3, or (at your option) any later | |
8 | version. | |
9 | ||
10 | GCC is distributed in the hope that it will be useful, but WITHOUT ANY | |
11 | WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
12 | FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
13 | for more details. | |
14 | ||
15 | Under Section 7 of GPL version 3, you are granted additional | |
16 | permissions described in the GCC Runtime Library Exception, version | |
17 | 3.1, as published by the Free Software Foundation. | |
18 | ||
19 | You should have received a copy of the GNU General Public License and | |
20 | a copy of the GCC Runtime Library Exception along with this program; | |
21 | see the files COPYING3 and COPYING.RUNTIME respectively. If not, see | |
22 | <http://www.gnu.org/licenses/>. */ | |
23 | ||
24 | /* This file is part of the vtable verification feature (for a | |
25 | detailed description of the feature, see comments in | |
26 | vtable-verify.c). The vtable verification feature creates | |
27 | certain global symbols that need to be read-write sometimes during | |
28 | program execution, and read-only at others. It uses 'mprotect' to | |
29 | change the memory protections of the pages on which these variables | |
30 | are stored. In order to not affect the protections of other | |
31 | program variables, these variables are put into a special named | |
32 | section, ".vtable_map_vars", which is page-aligned at the start, | |
33 | and which is padded with a page-sized amount of zeros at the end. | |
34 | To make this section page aligned, we create a special symbol, | |
35 | "_vtable_map_vars_start" which we make the very first thing that | |
36 | goes into the section. This file defines that symbol (and only | |
37 | that symbol). GCC compiles this file into vtv_start.o, and | |
38 | inserts vtv_start.o into the link line immediately after | |
39 | crtbegin.o, if the program is compiled with -fvtable.verify. | |
40 | ||
41 | In order to pad the ".vtable_map_vars" section with a page-sized | |
42 | amount of zeros at the end, there is a second symbol, | |
43 | _vtable_map_vars_end, which is defined in another file, vtv_end.c. | |
44 | This second symbol is a page-sized array of chars, zero-filled, and | |
45 | is the very last thing to go into the section. When the GCC driver | |
46 | inserts vtv_start.o into the link line (just after crtbegin.o) it | |
47 | also inserts vtv_end.o into the link line, just before crtend.o. | |
48 | This has the desired effect of making our section page-aligned and | |
49 | page-size paded, ensuring that no other program data lands on our | |
50 | pages. */ | |
51 | ||
52 | #include "vtv-change-permission.h" | |
53 | ||
54 | void | |
55 | __VLTUnprotectPreinit (void) | |
56 | { | |
57 | __VLTChangePermission (__VLTP_READ_WRITE); | |
58 | } | |
59 | ||
60 | /* Page-aligned symbol to mark beginning of .vtable_map_vars section. */ | |
61 | char _vtable_map_vars_start [] | |
62 | __attribute__ ((__visibility__ ("protected"), used, aligned(VTV_PAGE_SIZE), | |
63 | section(".vtable_map_vars"))) | |
64 | = { }; | |
65 | ||
66 | ||
67 | /* Put the function __VLTUnprotectPreinit into the .preinit_array | |
68 | section. */ | |
69 | ||
70 | __attribute__ ((section (".preinit_array"))) | |
71 | typeof (__VLTUnprotectPreinit) *__preinit = __VLTUnprotectPreinit; | |
72 |