Where do arguments come from?
The Game Boy Advance runs an ARM7TDMI, and these lessons compile to its compact Thumb instruction set. The first integer argument arrives in r0 — the very same register a function hands its result back in. That overlap has a funny consequence: a few functions give the compiler nothing to emit beyond the return.
bx lr
One bx lr, and that is a whole valid function. Further integer and pointer arguments stack up in r1, r2, and r3; anything past the fourth spills onto the stack. The return address rides in lr, the link register, so bx lr is simply "branch back to whoever called us".
So when the assembly is just a bx lr with nothing touching r0, here is the question to ask: what would the input and output have to be for no work to be needed at all?
Your task
Write identity, taking an int x, to reproduce the assembly above.