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Editorial Team
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Asked: 2026-06-06T04:53:10+00:00

We run code from adress 8002000 to 80020028 and the question is what is

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We run code from adress 8002000 to 80020028 and the question is what is inside register $18 at when we are at the end. I think there might be 0x0E but I am really not sure how i got to this answer anymore. Anyone can explain?

And if we start at 80020000 and follow the instructions as written can an exception occur? If yes when can it occur?

8001FFF8    NOP 
8001FFFC    NOP
80020000    LUI     $16, 0x8002
80020004    ADDIU   $16, $16, 0x30
80020008    ADDI    $17, $00, 0x3
8002000c    SLL     $17, $17, 0x2
80020010    LW      $18, 0x4 ($16)
80020014    LW      $19, 0x0 ($16)
80020018    SW      $18, 0x8 ($16)
8002001C    NOP
80020020    ADD     $18, $18, $17
80020024    NOP
80020028    NOP
8002002C    NOP
80020030    ???
80020034    SRL     $00, $00, 0
80020038    SRA     $00, $00, 0
8002003C    SLLV    $00, $00, $00
80020040    NOP
80020044    NOP
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1 Answer

  1. Editorial Team
    8001FFF8    NOP 
8001FFFC    NOP
80020000    LUI     $16, 0x8002
80020004    ADDIU   $16, $16, 0x30

    $16 = 0x80020030

    80020008    ADDI    $17, $00, 0x3
8002000c    SLL     $17, $17, 0x2

    $17 = 12 ( 3 << 2 )

    80020010    LW      $18, 0x4 ($16)

    $18 = 0x2 ( load value from 80020034 which disassembled is srl $0,$0,0 -> 0x2 )

    80020014    LW      $19, 0x0 ($16)

    $19 = ??? ( value under 0x80020030 not known )

    80020018    SW      $18, 0x8 ($16)

    store under 0x80020038 (0x2)

    8002001C    NOP
80020020    ADD     $18, $18, $17

    $18 = 0xE ( 0x2 + 12 )

    80020024    NOP
80020028    NOP

    $18 = 0xE ( nops don’t change anything )

    8002002C    NOP
80020030    ???
80020034    SRL     $00, $00, 0
80020038    SRA     $00, $00, 0
8002003C    SLLV    $00, $00, $00
80020040    NOP
80020044    NOP

    Exception in this code is possible ( I could miss something ):

    • at 80020018 sw instruction, if address if this fragment of memory is write-protected ( segmentation fault )
    • at 80020030 if executing code continues and execute this address ( illegal instruction )
    • at 80020010 if this fragment of memory is read-protected (very unlikely) ( segmentation fault )
    • at 80020000 if this fragment of memory is non-executable ( unlikely ) ( segmentation fault )
    • if addresses visible in this dump are not these visible by process which executes this code.. – hard to say without knowing environment and how this dump was got.
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