Assembly

What does this instruction do?

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Join Date: Jun 2008

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SirDorius

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What does this instruction do?

Jun 10th, 2008

Hello all! I'm new here

I was looking through a program and I was wondering what this instruction is:

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LEA EAX,DWORD PTR SS:[EBP-34]
LEA EAX,DWORD PTR SS:[EBP-34]

I know that LEA moves the offset of the second argument into EAX but I don't understand the segund argument very much:

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 Assembly Syntax (Toggle Plain Text) 
DWORD PTR SS:[EBP-34]
DWORD PTR SS:[EBP-34]

I'm guessing it's a pointer to a double word located in [EBP-34], but what does the SS stand for (no nazi jokes :p)?

And besides, what's the point in moving the offset of a pointer? Couldn't it just move the pointer directly, since it has the same size, and it wouldn't have to dereference it again afterwards

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Salem

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Void main'ers are DOOMed

Re: What does this instruction do?

Jun 10th, 2008

SS means stack segment.

EBP typically moves around with ESP (BP=Base Pointer, SP=Stack Pointer).

The BP is typically used to establish a fixed point of reference for a stack frame. BP + offset would typically be parameters, BP - offset would be local variables and temporary storage.

If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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