66 lines
2.9 KiB
C
66 lines
2.9 KiB
C
|
/* Copyright (C) 2012, 2013
|
||
|
|
Free Software Foundation, Inc.
|
||
|
|
|
||
|
|
This file is part of GCC.
|
||
|
|
|
||
|
|
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.
|
||
|
|
|
||
|
|
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.
|
||
|
|
|
||
|
|
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.
|
||
|
|
|
||
|
|
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/>. */
|
||
|
|
|
||
|
|
/* 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.
|
||
|
|
|
||
|
|
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. */
|
||
|
|
|
||
|
|
#include "vtv-change-permission.h"
|
||
|
|
|
||
|
|
__attribute__ ((constructor(98))) void
|
||
|
|
__VLTunprotect (void)
|
||
|
|
{
|
||
|
|
__VLTChangePermission (__VLTP_READ_WRITE);
|
||
|
|
}
|
||
|
|
|
||
|
|
/* 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")))
|
||
|
|
= { };
|