Use printf("%s", str); to avoid glibc assertion

runtime/vm/log.cc

 // Copyright (c) 2015, 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/log.h"
 
 #include "vm/flags.h"
 #include "vm/thread.h"
 
 namespace dart {
@@ skipping 41 matching lines @@
   }
   if (buffer_.is_empty()) {
     return;
   }
   if (buffer_.length() <= cursor) {
     return;
   }
   TerminateString();
   const char* str = &buffer_[cursor];
   ASSERT(str != NULL);
-  printer_(str);
+  printer_("%s", str);
   buffer_.TruncateTo(cursor);
 }
 
 
 void Log::Clear() {
   if (this == NoOpLog()) {
     return;
   }
   buffer_.TruncateTo(0);
 }
@@ skipping 44 matching lines @@
 
 
 LogBlock::LogBlock(Thread* thread)
     : StackResource(thread->isolate()),
       log_(thread->isolate()->Log()),
       cursor_(thread->isolate()->Log()->cursor()) {
   CommonConstructor();
 }
 
 }  // namespace dart