0,0 → 1,72 |
/* Copyright (C) 2012-2015 Free Software Foundation, Inc. |
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This file is part of GCC. |
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GCC is free software; you can redistribute it and/or modify it under |
the terms of the GNU General Public License as published by the Free |
Software Foundation; either version 3, or (at your option) any later |
version. |
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GCC 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 General Public License |
for more details. |
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Under Section 7 of GPL version 3, you are granted additional |
permissions described in the GCC Runtime Library Exception, version |
3.1, as published by the Free Software Foundation. |
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You should have received a copy of the GNU General Public License and |
a copy of the GCC Runtime Library Exception along with this program; |
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see |
<http://www.gnu.org/licenses/>. */ |
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/* This file is part of the vtable verification feature (for a |
detailed description of the feature, see comments in |
vtable-verify.c). The vtable verification feature creates |
certain global symbols that need to be read-write sometimes during |
program execution, and read-only at others. It uses 'mprotect' to |
change the memory protections of the pages on which these variables |
are stored. In order to not affect the protections of other |
program variables, these variables are put into a special named |
section, ".vtable_map_vars", which is page-aligned at the start, |
and which is padded with a page-sized amount of zeros at the end. |
To make this section page aligned, we create a special symbol, |
"_vtable_map_vars_start" which we make the very first thing that |
goes into the section. This file defines that symbol (and only |
that symbol). GCC compiles this file into vtv_start.o, and |
inserts vtv_start.o into the link line immediately after |
crtbegin.o, if the program is compiled with -fvtable.verify. |
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In order to pad the ".vtable_map_vars" section with a page-sized |
amount of zeros at the end, there is a second symbol, |
_vtable_map_vars_end, which is defined in another file, vtv_end.c. |
This second symbol is a page-sized array of chars, zero-filled, and |
is the very last thing to go into the section. When the GCC driver |
inserts vtv_start.o into the link line (just after crtbegin.o) it |
also inserts vtv_end.o into the link line, just before crtend.o. |
This has the desired effect of making our section page-aligned and |
page-size paded, ensuring that no other program data lands on our |
pages. */ |
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#include "vtv-change-permission.h" |
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void |
__VLTUnprotectPreinit (void) |
{ |
__VLTChangePermission (__VLTP_READ_WRITE); |
} |
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/* Page-aligned symbol to mark beginning of .vtable_map_vars section. */ |
char _vtable_map_vars_start [] |
__attribute__ ((__visibility__ ("protected"), used, aligned(VTV_PAGE_SIZE), |
section(".vtable_map_vars"))) |
= { }; |
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/* Put the function __VLTUnprotectPreinit into the .preinit_array |
section. */ |
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__attribute__ ((section (".preinit_array"))) |
typeof (__VLTUnprotectPreinit) *__preinit = __VLTUnprotectPreinit; |
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