Homework: Hardware/Software Virtualization

Submit two items to the the submission web site:

Submit your own question about the paper (e.g., what you find most confusing about the paper or the paper's general context/problem) before 11:59pm the night before. You cannot use the question below. To the extent possible, during lecture we will try to answer questions submitted the evening before.
Submit your answer for the question below before the beginning of the lecture

Answer the following question: The translated version of isPrime shown towards the end of Section 3.2 of the Adams/Agesen paper does not end with a ret instruction; instead, it ends with a jmp through %gs. What return instruction pointer is on the stack when isPrime starts, and why can't the translated isPrime return directly to that address?