LLVM, ZKVM, ELF

Summary of the full flow of zkvm compiling

Stage	What happens	Output
1. Compilation	Rust → LLVM IR → RISC-V machine code	ELF file
2. Parsing / loading	zkVM loads ELF into memory	memory layout
3. Execution / simulation	zkVM runs RISC-V instructions symbolically	execution trace
4. Constraint generation	Each step → algebraic constraint	AIR / PLONK polynomials
5. Proof generation	Apply STARK/SNARK	zk-proof
6. Verification	Verify proof on-chain or off-chain	✅ or ❌

Why RISC-V?

• Open standard — no licensing, anyone can implement it.
• Simple ISA — small number of instructions, easy to reason about in circuits.
• LLVM-supported — you can compile Rust, C, Go, etc. to RISC-V easily.
• Deterministic — good for reproducible computation proofs.

LLVM

LLVM is a compiler infrastructure that can turn code into optimized machine code for many architectures (x86, ARM, RISC-V, etc.).

What LLVM actually is

Think of LLVM as the middle and backend of a compiler pipeline.

If you imagine compiling code as a 3-stage process:

Stage	Name	What it does	Example
1️⃣	Frontend	Parses source code into syntax trees	Rust → rustc, C → clang
2️⃣	Optimizer / IR	Translates to intermediate representation (LLVM IR) and optimizes	LLVM
3️⃣	Backend	Generates target-specific machine code	x86, ARM, or RISC-V

How it connects to Rust

Rust uses LLVM internally.
When you run:

rustc main.rs

Rustc does:

1. Parse your code
2. Build the abstract syntax tree
3. Generate LLVM IR
4. Ask LLVM to optimize it
5. Ask LLVM to emit machine code for your chosen target (x86, ARM, RISC-V, WebAssembly, etc.)

That’s why you can cross-compile Rust easily:

rustc --target=riscv32im-unknown-none-elf main.rs

→ It just tells LLVM to emit RISC-V machine code instead of x86.

LLVM IR (Intermediate Representation) is the same language for all frontends that use LLVM —
but each high-level language might generate it a little differently depending on its semantics.