Guard against frames across pages, in the profiler.

runtime/vm/profiler.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/utils.h"
 
 #include "vm/allocation.h"
 #include "vm/atomic.h"
 #include "vm/code_patcher.h"
 #include "vm/isolate.h"
@@ skipping 1669 matching lines @@
       // Not walking the stack, only took exclusive sample.
       return 1;
     }
     uword* pc = reinterpret_cast<uword*>(original_pc_);
     uword* fp = reinterpret_cast<uword*>(original_fp_);
     uword* previous_fp = fp;
     if (original_sp_ > original_fp_) {
       // Stack pointer should not be above frame pointer.
       return 1;
     }
-    intptr_t gap = original_fp_ - original_sp_;
+    const intptr_t gap = original_fp_ - original_sp_;
     if (gap >= kMaxStep) {
       // Gap between frame pointer and stack pointer is
       // too large.
       return 1;
     }
     if (original_sp_ < lower_bound_) {
       // The stack pointer gives us a better lower bound than
       // the isolates stack limit.
       lower_bound_ = original_sp_;
     }
-    // Store the PC marker for the top frame.
-    sample_->set_pc_marker(GetCurrentFramePcMarker(fp));
+#if defined(TARGET_OS_WINDOWS)
+    // If the original_fp_ is at the beginning of a page, it may be unsafe
+    // to access the pc marker, because we are reading it from a different
+    // thread on Windows. The next page may be a guard page.
+    const intptr_t kPageMask = kMaxStep - 1;
+    bool safe_to_read_pc_marker = (original_fp_ & kPageMask) != 0;
+#else
+    bool safe_to_read_pc_marker = true;
+#endif
+    if (safe_to_read_pc_marker && (gap > 0)) {
+      // Store the PC marker for the top frame.
+      sample_->set_pc_marker(GetCurrentFramePcMarker(fp));
+    }
     int i = 0;
     for (; i < FLAG_profile_depth; i++) {
       if (FLAG_profile_verify_stack_walk) {
         VerifyCodeAddress(heap, i, reinterpret_cast<uword>(pc));
       }
       sample_->SetAt(i, reinterpret_cast<uword>(pc));
       if (fp == NULL) {
         return i + 1;
       }
       if (!ValidFramePointer(fp)) {
@@ skipping 118 matching lines @@
       ProfilerDartStackWalker stackWalker(sample);
       stackWalker.walk();
     } else {
       // TODO(johnmccutchan): Support collecting only Dart frames with
       // ProfilerNativeStackWalker.
     }
   }
 }
 
 }  // namespace dart