1 files changed, 59 insertions, 0 deletions
diff --git a/libgcc/vtv_start.c b/libgcc/vtv_start.c
new file mode 100644
index 00000000000..7899fdbd643
--- /dev/null
+++ b/libgcc/vtv_start.c
@@ -0,0 +1,59 @@
+/*  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.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  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
+   tree-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.  */
+
+#ifdef BIG_PAGE_SIZE
+/* TODO - Replace '4096' below with correct big page size.  */
+#define VTV_PAGE_SIZE 4096
+#else 
+#define VTV_PAGE_SIZE 4096
+#endif
+
+/* 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")))
+  = { };