12.2.3 Stack Frame Organization | Summary and Q&A

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July 12, 2019
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12.2.3 Stack Frame Organization

TL;DR

This content explains how activation records and stack frames work in procedures, including the allocation of arguments, local variables, and return addresses on the stack.

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Key Insights

  • 🥹 Activation records in procedures hold important data like arguments and local variables, allocated on the stack.
  • 🤙 The stack is used to save the return address and facilitate nested procedure calls.
  • 📲 The calling and called procedures share the responsibility for allocating and deallocating the activation record.
  • 🫷 Arguments are pushed on the stack in reverse order for easy access in variable argument procedures.
  • 😥 The base pointer is utilized to point to the current stack frame and simplify accessing values in the activation record.
  • 🍧 Having fixed offsets from the base pointer ensures straightforward access to arguments and local variables at compile time.
  • 👨‍💻 The base pointer is not strictly necessary, but using it for stack frame references makes the generated code more understandable.

Transcript

We'll use the stack to hold a procedure's activation record. That includes the values of the arguments to the procedure call. We'll allocate words on the stack to hold the values of the procedure's local variables, assuming we don't keep them in registers. And we'll use the stack to save the return address (passed in LP) so the procedure can make n... Read More

Questions & Answers

Q: What does the stack hold in a procedure's activation record?

The stack holds the values of arguments, local variables, and return addresses in a procedure's activation record.

Q: How are arguments pushed onto the stack in a procedure call?

Arguments are pushed onto the stack in reverse order, meaning the first argument is pushed last, to allow for easy access and handling of variable argument procedures.

Q: What is the purpose of the base pointer (BP) in the stack frame?

The base pointer is used to point to the current stack frame being built, making it easier to access values stored in the activation record.

Q: How does having a base pointer benefit accessing arguments and local variables?

Having a base pointer allows for fixed offsets from the base pointer to access arguments and local variables, making it easier and more efficient at compile time.

Summary & Key Takeaways

  • Activation records in procedures hold the values of arguments, local variables, and return addresses, allocated on the stack.

  • The responsibility for allocating and deallocating the activation record is shared between the calling and called procedures.

  • Arguments are pushed on the stack in reverse order, allowing for easy access and handling of variable argument procedures like printf.

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