imple
b008b37d49
Add a Tutorial tree that mirrors the roadmap from Phase 0 through Linux bring-up. Each phase and subphase gets a short learning note with consistent sections for context, goals, new concepts, mental model, learning tasks, pitfalls, tooling, testing, and references. The tutorial material is intentionally explanatory rather than implementation code. It gives a systems-oriented learner enough FPGA, SystemVerilog, RISC-V, firmware, and Linux bring-up context to approach each roadmap phase without turning the notes into copy-paste RTL.
50 lines
1.5 KiB
Markdown
50 lines
1.5 KiB
Markdown
# Phase 8.2 - First GCC Program
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## Context
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The first compiled program proves your hardware can execute compiler-generated code, not
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just carefully hand-authored assembly.
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## Goals
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- Compile a tiny C firmware for `rv32im`.
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- Convert the ELF into a memory image.
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- Print through UART MMIO from C.
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## New Concepts
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- `-march`: compiler ISA target string.
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- `-mabi`: ABI selection, here `ilp32` for 32-bit integer/long/pointer.
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- objcopy: tool that converts ELF into raw binary or other formats.
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- Disassembly: readable assembly representation of generated machine code.
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## How To Think About It
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Treat the compiler as an external producer of instructions. Your job is to verify that
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every emitted instruction is implemented or fails loudly.
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## Learning Tasks
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- Compare C source to generated assembly.
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- Identify every load/store used for UART access.
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- Confirm no CSR or `fence.i` instructions appear before Phase 9.
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## Pitfalls
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- Using the wrong `-march` and accidentally generating unsupported instructions.
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- Forgetting `volatile` on MMIO accesses in firmware.
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- Assuming the compiler will preserve simple-looking loops exactly.
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## Tooling And Testing
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- Always inspect early firmware with objdump.
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- Build at low optimization first, then compare optimized output later.
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- Keep firmware small enough to single-step mentally.
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## References
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- GCC RISC-V options: https://gcc.gnu.org/onlinedocs/gcc/RISC-V-Options.html
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- RISC-V ELF psABI: https://github.com/riscv-non-isa/riscv-elf-psabi-doc
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- GNU objcopy: https://sourceware.org/binutils/docs/binutils/objcopy.html
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