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assemblyx86attaddressing-mode

lea assembly instruction

I Just want to make sure I am reading this right:

movl 12(%ebp), %edx
leal (%edx, %edx, 4), %eax

I read the first line as: edx = [epb + 12], and the second line as: eax = edx + edx*4

Can anybody clarify?

Also, what if I had the following two lines:

leal (%edx, %edx, 4), %eax
leal (%edx, %edx, 2), %eax

Once the second line is executed, would the eax register be overwritten?

And the eax = edx + edx*4 is multiplying the address by 4? Or the contents of the address by 4?

Solution

  • You're right. The LEA instruction is used to Load (the) Effective Address, and can be used for address arithmetic and sometimes also ordinary arithmetic, if you don't need the flags.