Fix GetStackSample to check for nullptr

src/profiler/tick-sample.cc

 // Copyright 2013 the V8 project 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 "src/profiler/tick-sample.h"
 
 #include "include/v8-profiler.h"
 #include "src/frames-inl.h"
 #include "src/msan.h"
 #include "src/simulator.h"
@@ skipping 196 matching lines @@
     // The frame is not setup, so it'd be hard to iterate the stack. Bailout.
     return false;
   }
 
   i::ExternalCallbackScope* scope = isolate->external_callback_scope();
   i::Address handler = i::Isolate::handler(isolate->thread_local_top());
   // If there is a handler on top of the external callback scope then
   // we have already entrered JavaScript again and the external callback
   // is not the top function.
   if (scope && scope->scope_address() < handler) {
+    i::Address* external_callback_entry_ptr =
+        scope->callback_entrypoint_address();
     sample_info->external_callback_entry =
-        *scope->callback_entrypoint_address();
+        external_callback_entry_ptr == nullptr ? nullptr
+                                               : *external_callback_entry_ptr;
   }
 
   i::SafeStackFrameIterator it(isolate, reinterpret_cast<i::Address>(regs->fp),
                                reinterpret_cast<i::Address>(regs->sp),
                                js_entry_sp);
 
   // If at this point iterator does not see any frames,
   // is usually means something is wrong with the FP,
   // e.g. it is used as a general purpose register in the function.
   // Bailout.
@@ skipping 31 matching lines @@
                       bool use_simulator_reg_state) {
   v8::TickSample::Init(reinterpret_cast<v8::Isolate*>(isolate), state,
                        record_c_entry_frame, update_stats,
                        use_simulator_reg_state);
   if (pc == nullptr) return;
   timestamp = base::TimeTicks::HighResolutionNow();
 }
 
 }  // namespace internal
 }  // namespace v8