Fix false-positive ASAN detection with the stack profiler on win64

base/profiler/native_stack_sampler_win.cc

Index: base/profiler/native_stack_sampler_win.cc
diff --git a/base/profiler/native_stack_sampler_win.cc b/base/profiler/native_stack_sampler_win.cc
index 063374f19d5b1edfd7d758d98e4047a1b8d67bd6..283abdd4c6fbeedb11040c912eb4bcb9f2c18a1b 100644
--- a/base/profiler/native_stack_sampler_win.cc
+++ b/base/profiler/native_stack_sampler_win.cc
@@ -319,7 +319,7 @@ void SuspendThreadAndRecordStack(
     void* stack_copy_buffer,
     size_t stack_copy_buffer_size,
     std::vector<RecordedFrame>* stack,
-    NativeStackSamplerTestDelegate* test_delegate) {
+    NativeStackSamplerTestDelegate* test_delegate) NO_SANITIZE("address") {
   DCHECK(stack->empty());
 
   CONTEXT thread_context = {0};
@@ -353,8 +353,12 @@ void SuspendThreadAndRecordStack(
     if (PointsToGuardPage(bottom))
       return;
 
-    std::memcpy(stack_copy_buffer, reinterpret_cast<const void*>(bottom),

[Mark Mentovai, 2016/11/15 16:52:04]

Can we keep this if !defined(ADDRESS_SANITIZER)? Standard libraries often
optimize memcpy in ways that compilers don’t for simple byte-at-a-time loops.

[etienneb, 2016/11/15 16:55:41]

I'm not against it. Typically we try to avoid ifdef and duplicate code.
But, It's true that compilers may optimize memcpy and the stack profiler may be
CPU sensitive.

-                top - bottom);
+    // The following loop is an inlined version of memcpy. The code must be
+    // inlined to avoid instrumentation when using ASAN (memory sanitizer). The
+    // stack profiler is generating false positive when walking the stack.
+    for (size_t pos = 0; pos < top - bottom; ++pos)
+      reinterpret_cast<char*>(stack_copy_buffer)[pos] =
+          reinterpret_cast<const char*>(bottom)[pos];
   }
 
   if (test_delegate)
@@ -385,7 +389,7 @@ class NativeStackSamplerWin : public NativeStackSampler {
     // reserved stack size is 1 MB and Chrome Windows threads currently always
     // use the default, but this allows for expansion if it occurs. The size
     // beyond the actual stack size consists of unallocated virtual memory pages
-    // so carries little cost (just a bit of wated address space).
+    // so carries little cost (just a bit of wasted address space).
     kStackCopyBufferSize = 2 * 1024 * 1024
   };