12.2.4 Compiling a Procedure | Summary and Q&A

TL;DR

This content explains how procedure calls work, including the actions taken by the caller and callee, as well as the management of activation records and stack frames.

Key Insights

• 🫷 Procedure calls involve specific steps taken by the caller and callee, including pushing arguments onto the stack and jumping to the return address.
• 🥇 The caller is responsible for removing argument values from the stack, while the callee removes any items it has placed on the stack.
• 😒 All registers except R0 are preserved by the callee for the caller's use.
• 🖼️ Stack frames and activation records are used to manage storage for each procedure call, with a new stack frame allocated for each call.
• ☢️ The current state of execution can be determined by examining the active stack frames, including identifying active procedure calls and their arguments and local variable values.
• 💐 Stack traces, which show the progress of the computation, can be useful in debugging and understanding program flow.
• 🤙 Some optimizing compilers may inline small non-recursive procedures to reduce the overhead of procedure calls.

Transcript

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Questions & Answers

Q: What actions does the caller take during a procedure call?

The caller pushes argument values onto the stack in reverse order and branches to the callee's entry point, placing the return address in the linkage pointer.

Q: What actions does the callee take during a procedure call?

The callee performs the intended computation, leaving the result in R0, and removes any items it has placed on the stack. It then jumps to the return address to transfer control back to the calling procedure.

Q: What is the responsibility of the caller regarding argument values?

The caller is responsible for removing the argument values from the stack, as they were pushed onto the stack by the caller.

Q: What registers are preserved by the callee for the caller's use?

All registers except R0 are preserved by the callee, so the caller can assume that any values placed in registers before a nested call will remain there when the nested call returns.

Summary & Key Takeaways

• Procedure calls involve the caller pushing argument values onto the stack in reverse order and branching to the callee's entry point, with the return address placed in the linkage pointer.

• The callee performs the intended computation, leaving the result in R0, and removes any items it has placed on the stack.

• The caller is responsible for removing the argument values from the stack, and all registers except R0 are preserved for the caller's use.