Where do arguments come from?
On the N64's calling convention, the first integer argument arrives in a0 — that's what the a stands for. The next three ride in a1, a2, and a3. The return value, as you know, leaves in v0.
Notice those are different registers. Argument in a0, answer out in v0 — so even a function that returns its input completely unchanged has one real job to do: get the value across.
or v0, a0, zero # v0 = a0 | 0 — a register-to-register copy
jr ra # return
nop
An or? MIPS has no dedicated copy instruction, so the compiler leans on the zero register again: OR a value with 0 and you get the value back, landed wherever you pointed the destination. Last lesson zero loaded your constants; this lesson it copies registers. Learn to spot or rd, rs, zero and read it simply as "rd = rs" — it's one of the most common lines in all of MIPS.
So when the body of a function is a single copy from an argument register to v0, ask: what C function would need only to hand its input back?
Your task
Write identity, taking an s32 x, to reproduce the assembly above.