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I noticed that in Assembly segments are used in opcodes.
Example:
MOV DWORD PTR SS:[EBP-30],30
I think that “PTR SS:” is used to specify that EBP-30 comes from the stack? (SS: stack segment)
Am I right or am I completely wrong? 🙂 And, could you please tell me the difference between the example above and
MOV DWORD PTR[EBP-30],30
And what about DS (data segment) used in opcodes?
There are two separate modifiers here,
DWORD PTRandSS:.The first one tells us that we want to store a word at the address pointed to. This is needed when the assembler cannot tell that from the operands of the instruction. Here
30could just as well be a byte to store.The
SS:is a segment prefix, saying that we want to use an address relative to the stack segment. In this case it isn’t strictly needed, because that is the default when using theESPorEBPregisters. So the second version of the instruction is identical to the first one.Had you used
EBXinstead ofEBPthere would have been a difference!