Prevent FX_OutOfMemoryTerminate() from being folded by the linker.

Copy base::debug::Alias() from Chromium. Use it to prevent ICF from
combining FX_OutOfMemoryTerminate() with similar functions.

BUG=chromium:860850

Change-Id: Ifccb05c0218f86e44b9bb235847e01383ec36b3f
Reviewed-on: https://pdfium-review.googlesource.com/37290
Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>

4 files changed, 70 insertions, 2 deletions

diff --git a/core/fxcrt/fx_memory.cpp b/core/fxcrt/fx_memory.cpp
index 006e03031e..4c7b36855c 100644
--- a/core/fxcrt/fx_memory.cpp
+++ b/core/fxcrt/fx_memory.cpp
@@ -4,10 +4,11 @@
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
+#include <stdlib.h>  // For abort().
+
 #include "core/fxcrt/fx_memory.h"
 #include "core/fxcrt/fx_safe_types.h"
-
-#include <stdlib.h>  // For abort().
+#include "third_party/base/debug/alias.h"
 
 pdfium::base::PartitionAllocatorGeneric gArrayBufferPartitionAllocator;
 pdfium::base::PartitionAllocatorGeneric gGeneralPartitionAllocator;
@@ -45,6 +46,11 @@ void FXMEM_DefaultFree(void* pointer) {
 }
 
 NEVER_INLINE void FX_OutOfMemoryTerminate() {
+  // Convince the linker this should not be folded with similar functions using
+  // Identical Code Folding.
+  static int make_this_function_aliased = 0xbd;
+  base::debug::Alias(&make_this_function_aliased);
+
   // Termimate cleanly if we can, else crash at a specific address (0xbd).
   abort();
 #ifndef _WIN32
diff --git a/third_party/BUILD.gn b/third_party/BUILD.gn
index 8b212e1622..847229273e 100644
--- a/third_party/BUILD.gn
+++ b/third_party/BUILD.gn
@@ -554,6 +554,8 @@ jumbo_source_set("pdfium_base") {
     "base/base_export.h",
     "base/bits.h",
     "base/compiler_specific.h",
+    "base/debug/alias.cc",
+    "base/debug/alias.h",
     "base/logging.h",
     "base/macros.h",
     "base/numerics/safe_conversions.h",
diff --git a/third_party/base/debug/alias.cc b/third_party/base/debug/alias.cc
new file mode 100644
index 0000000000..3ab554fe48
--- /dev/null
+++ b/third_party/base/debug/alias.cc
@@ -0,0 +1,28 @@
+// Copyright (c) 2011 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.
+
+#include "third_party/base/debug/alias.h"
+
+#include "build/build_config.h"
+
+namespace base {
+namespace debug {
+
+#if defined(COMPILER_MSVC)
+#pragma optimize("", off)
+#elif defined(__clang__)
+#pragma clang optimize off
+#endif
+
+void Alias(const void* var) {
+}
+
+#if defined(COMPILER_MSVC)
+#pragma optimize("", on)
+#elif defined(__clang__)
+#pragma clang optimize on
+#endif
+
+}  // namespace debug
+}  // namespace base
diff --git a/third_party/base/debug/alias.h b/third_party/base/debug/alias.h
new file mode 100644
index 0000000000..4d02e7af74
--- /dev/null
+++ b/third_party/base/debug/alias.h
@@ -0,0 +1,32 @@
+// Copyright (c) 2011 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.
+
+#ifndef BASE_DEBUG_ALIAS_H_
+#define BASE_DEBUG_ALIAS_H_
+
+namespace base {
+namespace debug {
+
+// Make the optimizer think that var is aliased. This is to prevent it from
+// optimizing out local variables that would not otherwise be live at the point
+// of a potential crash.
+// base::debug::Alias should only be used for local variables, not globals,
+// object members, or function return values - these must be copied to locals if
+// you want to ensure they are recorded in crash dumps.
+// Note that if the local variable is a pointer then its value will be retained
+// but the memory that it points to will probably not be saved in the crash
+// dump - by default only stack memory is saved. Therefore the aliasing
+// technique is usually only worthwhile with non-pointer variables. If you have
+// a pointer to an object and you want to retain the object's state you need to
+// copy the object or its fields to local variables. Example usage:
+//   int last_error = err_;
+//   base::debug::Alias(&last_error);
+//   DEBUG_ALIAS_FOR_CSTR(name_copy, p->name, 16);
+//   CHECK(false);
+void Alias(const void* var);
+
+}  // namespace debug
+}  // namespace base
+
+#endif  // BASE_DEBUG_ALIAS_H_