What is the strict aliasing rule?

struct Msg
{
   unsigned int a;
   unsigned int b;
};

int main()
{
   // Get a 32-bit buffer from the system
   uint32_t* buff = malloc(sizeof(Msg));

   // Alias that buffer through message
   Msg* msg = (Msg*)(buff);

   // Send a bunch of messages
   for (int i =0; i < 10; ++i)
   {
      msg->a = i;
      msg->b = i+1;
      SendWord(buff[0] );
      SendWord(buff[1] );

   }

}

void SendMessage(uint32_t* buff, size_t size32)
 {
    for (int i = 0; i < size32; ++i)
    {
       SendWord(buff[i]);
    }
 }

for (int i =0; i < 10; ++i)
   {
      msg->a = i;
      msg->b = i+1;
      SendMessage(buff, 2);
   }

char*