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Cs315 01 2025 09 04 summary

Quick recap The meeting focused on teaching assembly language programming concepts, particularly function calls, return addresses, and stack management. Greg explained the mechanics of function calls and returns, including how registers are updated and the importance of preserving return addresses on the stack to avoid errors. The discussion covered practical examples of implementing functions, managing stack space, and following register preservation conventions, with emphasis on proper stack management and defensive coding practices. Next steps Next steps were not generated due to insufficient transcript. Summary Function Calls and Control Flow Greg discussed the concept of complex functions, focusing on function calling and returning. He explained the role of the RA (Return Address) register, which is updated to hold the address of the next instruction after the call, and the PC (Program Counter) register, which is updated to point to the target function. Greg emphasized that a function call involves two main updates: updating the RA register and updating the PC register to change control flow. Call and Return Mechanisms Explained Greg explained the mechanics of call and return instructions, highlighting how they manipulate the program counter (PC) and use the return address (RA) to link the caller and callee. He noted that when a function calls another, the original RA is overwritten, leading to a problem when the original function tries to return. To solve this, Greg explained that the RA must be saved before a function call, which is achieved by using the stack, allowing the RA to be restored after the call and ensuring the correct return address is used. Stack Concepts in Assembly Programming Greg explained the concept of the stack in assembly programming, discussing how it is used for storing data and tracking return addresses. He described how to allocate and deallocate space on the stack using the stack pointer register (SP), emphasizing the need to allocate in multiples of 16 bytes. Greg also explained the typical pattern of stack allocation and deallocation in functions, highlighting the importance of matching the amount of space allocated with the amount deallocated to avoid errors. Register Saving Rules in Function Calls Greg explained the rules for saving registers in different function call scenarios, emphasizing that in some cases, the caller is responsible for saving registers like RA. He discussed the usage of various registers, including X0 (always 0), X1 (RA for function calls), X2 (SP for stack allocation), and others used for multi-threading. Greg clarified the distinction between caller-saved and callee-saved registers, explaining that caller-saved registers (A0-A7, T0-T6, RA) are modified by the caller, while callee-saved registers (S0-S11, SP) are modified by the callee and must be preserved. He concluded by noting that they would next explore how to store and restore values on the stack, using memory instructions they had previously learned. Stack Memory and Pointer Management Greg discussed stack memory allocation and manipulation, explaining how to store and retrieve values using stack pointers and addressing modes. He demonstrated that on a 64-bit machine, pointers require 8 bytes (double words) rather than 4 bytes, and showed how to allocate 16 bytes of stack space to store a double-word value. Greg also covered the process of saving and restoring registers, including the use of the S0 register, and explained how to properly manage stack space by both allocating and deallocating memory when entering and exiting functions. Caller Saved Registers and Conventions Greg discussed the concept of caller and colleague saved registers, explaining how they are used in function calls and the importance of following conventions strictly, even in simple cases. He clarified that while it's possible to load a return address after a call, it's generally better to restore it at the end of the method to avoid unnecessary overhead. Greg then demonstrated this with a basic "Hello, World" example in assembly language, emphasizing the need to assume the worst-case scenario when writing defensive code and following conventions rigorously, especially when making library calls. Assembly Function Call Stack Management Greg explained how to handle function calls and returns in assembly language, focusing on preserving the return address (RA) on the stack to avoid infinite loops. He demonstrated the correct implementation using gdb to step through the code and showed how to allocate stack space, store RA, perform the function call, and restore RA before returning. The discussion included practical examples of debugging and fixing issues with function calls, emphasizing the importance of proper stack management. Assembly Language Programming Basics Greg explained the lowest software level of programming, using assembly language to demonstrate how functions are implemented and registers are managed. He showed an example of a function that adds four numbers using three calls to a simpler add function, emphasizing the importance of preserving caller-safe registers and managing stack space. Greg highlighted the need to temporarily store return values and maintain the order of operations to ensure correct results. He mentioned that he would review the code the next day and discuss recursion. Code Review and Stack Management Greg discussed the process of reviewing and refining code, focusing on function calls and stack management. He emphasized the importance of asking specific questions about arguments and caller state registers to determine what should be placed on the stack. Greg also explained the difference between computing the maximum value directly in a loop and writing a function to find the maximum of two values, using a ternary operator to set up the assembly code. Assembly Code Conversion Challenges Greg discussed the challenges of converting assembly code to a version that includes calls, particularly focusing on the complexity introduced by caller-saved registers and the need to preserve and restore registers correctly. He emphasized the importance of understanding stack management, allocating the right amount of space, and following rules such as saving registers in multiples of 16. Greg suggested starting with logic in assembly without worrying about register preservation, then addressing it after the logic is clear. He encouraged students to think through the process and seek help if needed, with June and Greg available for assistance. Compiler Analysis and Assembly Integration Greg discussed the complexity of compiler analysis and register management in assembly code, emphasizing that compilers handle much of the heavy lifting. He provided guidance on integrating assembly code into a project, suggesting students start by incorporating their assembly code from lab exercises and adding necessary components like Max. Greg also addressed questions about using registers, clarifying that while it's common to reset registers, students should follow the specific instructions provided. He encouraged students to reach out if they need updates or have questions about the code, and mentioned that he had recently pushed updates to the repository. Register Allocation in Assembly Programming Greg discussed the use of registers in assembly language programming, emphasizing the importance of thinking about register allocation as if writing the code from scratch. He clarified that when allocating space on the stack, the stack pointer (SP) is used to determine where to store data, but SP itself is not stored in memory. Greg also addressed issues with accessing Zoom recordings through SSO authentication and explained how to allocate and manage space on the stack, including preserving the SP by accounting for the amount of space deallocated.# CS 315-01 Lecture/Lab — Meeting Summary (Fall 2025)

Meeting Details

  • Date: Sep 04, 2025
  • Time: 08:09 AM Pacific (US and Canada)
  • Zoom ID: 886 4953 2573

Quick Recap

The session introduced programming fundamentals with a focus on assembly language and function implementation in both C and assembly. Greg demonstrated: - Memory operations, register usage, and array handling - Data processing, control instructions, and memory management - Conditional branching and loop structures - Practical examples of if-else statements and simple loops

Action Items (Next Steps)

  • Pull the in-class repository for the Lab 3 starter files.
  • Pull the latest test repository for updated tests.
  • Complete Lab 3 exercises on functions, arrays, and control statements in assembly.
  • For Lab 3, use only A registers and T registers.
  • Practice array access in assembly using load word (lw) instructions.
  • Review if statements and loops for Lab 3.
  • Review the RISC-V register cheat sheet.
  • Remove placeholder comments from the starter code.
  • Mac users: Install iTerm for improved key functionality.
  • Optional resource: Browse Hacker News for computer science news.

Detailed Summary

Introduction to Programming and Assembly

Greg emphasized understanding functions, return values, and control flow (if statements, loops). He demonstrated implementing functions in both C and assembly using provided starter code. He also showed editor features (tabs and panes) to support coding workflows and walked through a simple assembly function.

Assembly Programming Register Conventions

  • Emphasis on using the A and T register sets for simplicity in this lab.
  • Demonstrated basic arithmetic in functions.
  • Introduced passing arrays as arguments rather than individual values.
  • Reviewed the three instruction categories: data processing, control, and memory.
  • Noted that function calls will be covered next week.

Computer Memory and Register Operations

  • Explained how computation involves moving data from memory to registers before processing.
  • Demonstrated lw (load word) to fetch 32-bit values from memory.
  • Showed array access by offsetting the base address by 4 bytes per element.
  • Used a0 as the base address register and temporary registers for loaded values.

Assembly Code: Array Sum Demonstration

  • Demonstrated summing the first three array elements in assembly:
  • Load values from memory
  • Increment pointers/offsets
  • Accumulate and return the result
  • Clarified “Return” vs. “Enter” key terminology.
  • Recommended iTerm for Mac users.
  • Indicated that assembly discussion will continue in a later session.

Memory Access and Array Operations

  • Compared two approaches to the same addition:
  • Passing individual integers as arguments
  • Accessing values through array elements in memory
  • Highlighted the role of memory instructions like lw.
  • Announced a short break before transitioning to if statements and loops (required for Lab 3).

Zoom and GitHub Access Troubleshooting

  • Resolved access to Zoom recordings by using USF single sign-on instead of personal accounts.
  • Directed students to the class repository for Lab 3 even if GitHub organization access was pending.
  • Acknowledged ongoing GitHub access issues affecting some students.

Memory and Control Instructions Overview

  • Memory:
  • Arrays and integers in memory; integers are 4 bytes.
  • Addresses point to bytes.
  • Control:
  • Unconditional jumps and conditional jumps.
  • Labels specify jump targets.
  • Loops are built by combining labels and jumps to repeat instruction sequences.

Conditional Branching in Assembly

  • Introduced conditional branching with instructions like “branch if less than or equal” (e.g., ble).
  • Implemented an if-else pattern using labels and explicit branch targets.
  • Discussed handling negative numbers and understanding execution flow.

Assembly Loop Implementation Demonstration

  • Implemented a loop that sums values up to a given N.
  • Provided equivalent C code and mapped it to assembly with conditional branches and unconditional jumps.
  • Demonstrated running and stepping through the assembly in a debugger to verify output.