Does the ret instruction add 4 to esp register?

assembly x86 return instructions stack-pointer
remainn picture remainn · Nov 27, 2010 · Viewed 14.6k times · Source

Does the ret instruction cause "esp" register to be increased by 4?

Answer

ruslik picture ruslik · Nov 27, 2010

Yes, it performs 

pop eip

You can use 

mov eax, [esp]
jmp eax

to avoid it.

EDIT: It's exactly what ret does. For example, jmp rel_offet is nothing than a hidden add eip, offset, or jmp absolute_offset is mov eip, absolute_offset. Sure there are differences in the way the processor treats them, but from programmer's point of view it's all that happens.

Also, there is a special form of ret : ret imm8 that also adds this imm8 value to esp : for example a __stdcall function uses it to discard its parameters from the stack. Not to mention retf version, used in 16bit mode, that also pops the cs from the stack.

EDIT2:

pop register

means:

mov register, [esp]
add esp, 4

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