Catch corrupted pointers earlier.

runtime/vm/disassembler_x64.cc

 // Copyright (c) 2012, 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 "vm/disassembler.h"
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_IA32.
 #if defined(TARGET_ARCH_X64)
 #include "platform/utils.h"
 #include "vm/allocation.h"
@@ skipping 791 matching lines @@
   OS::SNPrint(chars, len, format, full_class_name);
   return chars;
 }
 
 
 void DisassemblerX64::AppendAddressToBuffer(uint8_t* addr_byte_ptr) {
   uword addr = reinterpret_cast<uword>(addr_byte_ptr);
   AppendToBuffer("%#" Px "", addr);
   // Try to print as heap object or stub name
   if (((addr & kSmiTagMask) == kHeapObjectTag) &&
+      reinterpret_cast<RawObject*>(addr)->IsWellFormed() &&
       reinterpret_cast<RawObject*>(addr)->IsOldObject() &&
       !Isolate::Current()->heap()->CodeContains(addr) &&
       Disassembler::CanFindOldObject(addr)) {
     NoGCScope no_gc;
     const Object& obj = Object::Handle(reinterpret_cast<RawObject*>(addr));
     if (obj.IsArray()) {
       const Array& arr = Array::Cast(obj);
       intptr_t len = arr.Length();
       if (len > 5) len = 5;  // Print a max of 5 elements.
       AppendToBuffer("  Array[");
@@ skipping 1123 matching lines @@
   }
   hex_buffer[hex_index] = '\0';
   if (out_instr_len) {
     *out_instr_len = instruction_length;
   }
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64