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assemblyx86y86

IA32 assembly code to Y86 assembly code: leal instruction


I am studying how to convert IA32 assembly code to Y86 assembly code, and I am stuck in the following instruction which is in IA32 code:

 leal(%edx, %eax), %eax

I cannot find the equivalent instructions for the Y86 code. I have though of two version as the following ones, but I am not sure which is right:

Version 1:

 mrmovl (%edx), %ebx
 mrmovl (%eax), %esi
 addl %ebx, %esi
 rrmovl %esi, 5eax

Version 2:

 addl %edx, %eax

Does anyone have a better idea?


Solution

  • LEA doesn't access memory, it only does (address) arithmetic. As such your version #2 is correct.

    Note that on x86 LEA doesn't affect flags, while ADD does. LEA also supports more complex effective address syntax, which is nevertheless quite straight-forward to transcribe to y86. For example,

    leal offset(%eax, %ebx, 4), %edx
    

    becomes:

    rrmovl %ebx, %edx
    addl %edx, %edx
    addl %edx, %edx
    addl %eax, %edx
    pushl %eax           # save eax which used as temporary for adding the offset
    irmovl $offset, %eax
    addl %eax, %edx
    popl %eax            # restore eax