port cfi to gn

build/config/BUILDCONFIG.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # =============================================================================
 # PLATFORM SELECTION
 # =============================================================================
 #
 # There are two main things to set: "os" and "cpu". The "toolchain" is the name
 # of the GN thing that encodes combinations of these things.
@@ skipping 127 matching lines @@
 
   # Compile for Leak Sanitizer to find leaks.
   is_lsan = false
 
   # Compile for Memory Sanitizer to find uninitialized reads.
   is_msan = false
 
   # Compile for Thread Sanitizer to find threading bugs.
   is_tsan = false
 
+  # Compile with Control Flow Integrity to protect virtual calls and casts.
+  # See http://clang.llvm.org/docs/ControlFlowIntegrity.html
+  is_cfi = false

[brettw, 2015/09/03 04:41:20]

I was thinking of removing the *san flags from here (trying to keep the global
file small). Doing this will require refactoring the symbol configuration a bit
that I was procrastinating on. But even more sanitizers makes me realize we
really need to do this.

In the mean time, can you move your flags to
build/config/sanitizers/sanitizers.gni and import that file when you need to use
the flags?

Until I clean up the symbols a CFI build will presumably need symbol_level=1 set
to work properly (assuming you really do need this level of symbols). You can
add an assert in the sanitizers.gni file that this is the case (maybe you can
also tolerate 2?) so people don't screw up.

Then you can do it with no changes to this file.

[pcc1, 2015/09/04 21:56:59]

Done.
The CFI build does not require symbols other than for better stack traces, so
the default is probably fine.

+
+  # Whether Control Flow Integrity prints diagnostics instead of crashing.
+  use_cfi_diag = false
+
   if (current_os == "chromeos") {
     # Allows the target toolchain to be injected as arguments. This is needed
     # to support the CrOS build system which supports per-build-configuration
     # toolchains.
     cros_use_custom_toolchain = false
   }
 
   # DON'T ADD MORE FLAGS HERE. Read the comment above.
 }
 
@@ skipping 273 matching lines @@
   _default_optimization_config = "//build/config/compiler:optimize"
 }
 _native_compiler_configs += [ _default_optimization_config ]
 
 # If it wasn't manually set, set to an appropriate default.
 if (symbol_level == -1) {
   # Linux is slowed by having symbols as part of the target binary, whereas
   # Mac and Windows have them separate, so in Release Linux, default them off.
   if (is_debug || !is_linux) {
     symbol_level = 2
-  } else if (is_asan || is_lsan || is_tsan || is_msan) {
+  } else if (is_asan || is_lsan || is_tsan || is_msan || is_cfi) {
     # Sanitizers require symbols for filename suppressions to work.
     symbol_level = 1
   } else {
     symbol_level = 0
   }
 }
 
 # Symbol setup.
 if (symbol_level == 2) {
   _default_symbols_config = "//build/config/compiler:symbols"
@@ skipping 166 matching lines @@
     forward_variables_from(invoker, "*")
 
     # All shared libraries must have the sanitizer deps to properly link in
     # asan mode (this target will be empty in other cases).
     if (!defined(deps)) {
       deps = []
     }
     deps += [ "//build/config/sanitizers:deps" ]
   }
 }