diff options
Diffstat (limited to 'libgcc/vtv_start_preinit.c')
-rw-r--r-- | libgcc/vtv_start_preinit.c | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/libgcc/vtv_start_preinit.c b/libgcc/vtv_start_preinit.c new file mode 100644 index 0000000..512c858 --- /dev/null +++ b/libgcc/vtv_start_preinit.c @@ -0,0 +1,73 @@ +/* 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" + +void +__VLTUnprotectPreinit (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"))) + = { }; + + +/* Put the function __VLTUnprotectPreinit into the .preinit_array + section. */ + +__attribute__ ((section (".preinit_array"))) + typeof (__VLTUnprotectPreinit) *__preinit = __VLTUnprotectPreinit; + |