/* Copyright (C) 2012-2022 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;