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What is the difference between iret and iretd, iretq?

I want to simulate an iret condition on an x86_64 Linux server. I found three instructions

  • iret: operand size 16
  • iretd: operand size 32
  • iretq: operand size 64

I can not distinguish them, and which one to use. thanks for the help!

I have another question about iret simulation, can you see? http://stackoverflow.com/questions/11756274/how-to-simulate-a-iret-on-linux-x86-64

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From this link :

An IRET is returned with an interrupt (hardware or software) using (or EIP), CS and flags from the stack, and then continuing execution from the new CS: IP.

IRETW issues IP, CS and flags of 2 bytes each, removing the 6 bytes stack as a whole. IRETD issues EIP as 4 bytes, produces 4 more bytes of which the two upper parts are discarded, and the lower two go to CS, and issues flags as 4 bytes, taking 12 bytes from the stack.

IRET is short for IRETW or IRETD, depending on the default BITS.

Very similar to IRETQ

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