ARMx32-C-Library-Integration

This repository contains ARMx32 assembly code for CSCO 2150: Computer Organization. This program shows how to call C library functions like printf and time directly from assembly.

This specific example focuses on using toupper() to demonstrate how to pass a character value into a function and get a result back using the gcc compiler.

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Logic Analysis

• Pointer vs. Value: The C documentation for toupper(int c) requires a value. In my code, I used ldrb to pass the actual character value, unlike time() which requires a memory address.
• Register Flow: I followed the ATPCS standard: input was passed in r0, and the uppercase result was retrieved from r0 after the call.
• Memory Size: I used ldrb (Load Byte) because characters are 1 byte. Using a standard ldr (4 bytes) would have loaded unintended data from adjacent memory.

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How to Build and Run

⚠️ Disclaimer: Architecture Compatibility

This code is written specifically for the ARMx32 (AArch32) architecture. It will not run natively on standard Intel or AMD (x86_64) processors. To run this code, you must use:

• An ARM-based device (e.g., Raspberry Pi, BeagleBone).
• An ARM emulator or virtual machine (e.g., QEMU).
• A cross-compiler if building on a non-ARM system. To compile using the GCC toolchain:

gcc program.s -o program
./program