Fix invalid pointer arithmetic in Linux and MacOS event handler

runtime/bin/eventhandler_linux.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 "bin/eventhandler.h"
 
 #include <errno.h>
 #include <pthread.h>
 #include <stdio.h>
 #include <string.h>
@@ skipping 150 matching lines @@
   if (result != kInterruptMessageSize) {
     if (result == -1) {
       perror("Interrupt message failure:");
     }
     FATAL1("Interrupt message failure. Wrote %d bytes.", result);
   }
 }
 
 
 bool EventHandlerImplementation::GetInterruptMessage(InterruptMessage* msg) {
+  char* dst = reinterpret_cast<char*>(msg);
   int total_read = 0;
   int bytes_read =
-      TEMP_FAILURE_RETRY(read(interrupt_fds_[0], msg, kInterruptMessageSize));
+      TEMP_FAILURE_RETRY(read(interrupt_fds_[0], dst, kInterruptMessageSize));
   if (bytes_read < 0) {
     return false;
   }
   total_read = bytes_read;
   while (total_read < kInterruptMessageSize) {
     bytes_read = TEMP_FAILURE_RETRY(read(interrupt_fds_[0],
-                                         msg + total_read,
+                                         dst + total_read,
                                          kInterruptMessageSize - total_read));
     if (bytes_read > 0) {
       total_read = total_read + bytes_read;
     }
   }
   return (total_read == kInterruptMessageSize) ? true : false;
 }
 
 void EventHandlerImplementation::HandleInterruptFd() {
   InterruptMessage msg;
@@ skipping 219 matching lines @@
 void* EventHandlerImplementation::GetHashmapKeyFromFd(intptr_t fd) {
   // The hashmap does not support keys with value 0.
   return reinterpret_cast<void*>(fd + 1);
 }
 
 
 uint32_t EventHandlerImplementation::GetHashmapHashFromFd(intptr_t fd) {
   // The hashmap does not support keys with value 0.
   return dart::Utils::WordHash(fd + 1);
 }