Interview prompt
Explain what a function call places in a stack frame to an engineer who understands the surrounding system but has not used this technique. Walk from its contract to a concrete operation, then discuss where it fails or becomes expensive.
A strong answer
A function call transfers control while preserving enough state for the caller to resume. A calling convention defines how arguments, return values, registers, and stack alignment are handled. A stack frame commonly holds saved registers, local storage, and bookkeeping, though optimizers can keep values in registers or remove frames.
When function A calls B, the machine records a return location and passes arguments according to the platform ABI. B may reserve stack space and save registers it must preserve. On return, it places the result where the caller expects and restores the control state required by the convention.
A complete answer also calls out the assumptions that control correctness. Recursion creates nested activation state and can exhaust a finite stack. Tail-call elimination can reuse a frame when language and compiler rules permit it, but should not be assumed across every runtime. Stack layout and calling conventions vary by architecture and compiler.
Close by describing one representative test or measurement. Trace a recursive function with input depth three. At each call, list the values that must remain available for the suspended caller after the deeper call returns.
Follow-up questions
Answer the follow-ups in the frontmatter. Use the linked article for the concept and the trace to make the explanation concrete.