Prevent sign extension for pointer trace values

base/trace_event/trace_event_impl.cc

 // Copyright (c) 2012 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 "base/trace_event/trace_event_impl.h"
 
 #include <stddef.h>
 
 #include "base/format_macros.h"
 #include "base/json/string_escape.h"
@@ skipping 243 matching lines @@
         real = "\"Infinity\"";
       }
       StringAppendF(out, "%s", real.c_str());
       break;
     }
     case TRACE_VALUE_TYPE_POINTER:
       // JSON only supports double and int numbers.
       // So as not to lose bits from a 64-bit pointer, output as a hex string.
       StringAppendF(
           out, "\"0x%" PRIx64 "\"",
-          static_cast<uint64_t>(reinterpret_cast<intptr_t>(value.as_pointer)));
+          static_cast<uint64_t>(reinterpret_cast<uintptr_t>(value.as_pointer)));

[caseq, 2016/06/09 16:59:13]

can we drop the inner one and do a reinterpret_cast<uint64_t>(value.as_pointer)
straight away?

[Kunihiko Sakamoto, 2016/06/10 05:19:24]

Unfortunately, that doesn't prevent sign extension.
http://stackoverflow.com/questions/22239752/convert-32-bit-pointer-to-64-bit-...
Looks like 2-step conversion is necessary.

       break;
     case TRACE_VALUE_TYPE_STRING:
     case TRACE_VALUE_TYPE_COPY_STRING:
       EscapeJSONString(value.as_string ? value.as_string : "NULL", true, out);
       break;
     default:
       NOTREACHED() << "Don't know how to print this value";
       break;
   }
 }
@@ skipping 142 matching lines @@
         AppendValueAsJSON(arg_types_[i], arg_values_[i], &value_as_text);
 
       *out << value_as_text;
     }
     *out << "}";
   }
 }
 
 }  // namespace trace_event
 }  // namespace base