# Phase 8.2 - First GCC Program

## Context

The first compiled program proves your hardware can execute compiler-generated code, not
just carefully hand-authored assembly.

## Goals

- Compile a tiny C firmware for `rv32im`.
- Convert the ELF into a memory image.
- Print through UART MMIO from C.

## New Concepts

- `-march`: compiler ISA target string.
- `-mabi`: ABI selection, here `ilp32` for 32-bit integer/long/pointer.
- objcopy: tool that converts ELF into raw binary or other formats.
- Disassembly: readable assembly representation of generated machine code.

## How To Think About It

Treat the compiler as an external producer of instructions. Your job is to verify that
every emitted instruction is implemented or fails loudly.

## Learning Tasks

- Compare C source to generated assembly.
- Identify every load/store used for UART access.
- Confirm no CSR or `fence.i` instructions appear before Phase 9.

## Pitfalls

- Using the wrong `-march` and accidentally generating unsupported instructions.
- Forgetting `volatile` on MMIO accesses in firmware.
- Assuming the compiler will preserve simple-looking loops exactly.

## Tooling And Testing

- Always inspect early firmware with objdump.
- Build at low optimization first, then compare optimized output later.
- Keep firmware small enough to single-step mentally.

## References

- GCC RISC-V options: https://gcc.gnu.org/onlinedocs/gcc/RISC-V-Options.html
- RISC-V ELF psABI: https://github.com/riscv-non-isa/riscv-elf-psabi-doc
- GNU objcopy: https://sourceware.org/binutils/docs/binutils/objcopy.html