What is wrong with the following instructions?

Question

Stuck on a question while looking over my past exam papers. The question reads 'What, if anything, is wrong with the following instructions?'

.text
   dadd r2,r0,10
   j r3
   dsub r4,r1,N(r0)

Answer 1

That would depend on which assembler you're using. But if we assume that you're using an assembler that looks at the instructions strictly as-is:

dadd r2,r0,10

The dadd instructions takes three registers as its operands. For the operands r2,r0,10 you would use daddi (doubleword add immediate).

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j r3

The j instruction expects an absolute address (i.e. j some_label). For register-indirect jumps you'd use the jr instruction.

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dsub r4,r1,N(r0)

Like dadd, dsub also takes three registers as its operands. As far as I know there's no variant of dsub that accepts a memory location as one of its operands. This instruction would have to be split in two (e.g. ld r4,N(r0), followed by dsub r4,r1,r4).