vysort 0.1.0

Make vyper 0.3.4-0.3.7 bytecode deterministic by forcing the internal-function layout

vysort

Make vyper 0.3.4–0.3.7 bytecode deterministic.

These compiler versions emit nondeterministic bytecode for any contract whose call graph contains a decision point — a function calling ≥2 internal functions defined later in the file (vyper#3369). The internal-function sections get permuted per environment (and per run on linux), which blocks byte-exact verification: the verifier's recompile may never reproduce what the deployer's machine happened to emit.

vysort fixes this with no compiler modifications: it decodes the deployed layout straight off the on-chain bytecode, then reorders the source so internal function defs come first, in that exact order. The topsort then has zero decision points and a stock compiler produces the deployed bytecode everywhere, every run.

Install

uv tool install vysort

Or run from a checkout: uv run vysort ...

vysort itself runs on any modern python and depends only on uv. The vyper-touching work runs in an ephemeral uv run environment with the matching compiler: the vyper version is auto-detected from the source's version pragma (override with --vyper), on python 3.10 by default (override with --python). No old python or vyper install needed.

Verify your contract

If your vyper 0.3.x contract fails verification, this is the command:

vysort verify contract.vy --address 0x2cced4ff... --rpc-url https://eth.drpc.org

It fetches the deployed code and chain id from the RPC, recovers the deployed internal-function layout from the on-chain bytes, rewrites the source to force that layout, confirms the exact standard-json payload reproduces the runtime byte-for-byte (a preflight compile through vyper's own std-json entry point — the same path the verifier's binary takes), and submits it to sourcify's v2 API with a stock compiler version. No forks, no patched binaries, no special verifier support.

Use --dry-run to inspect the submission payload without sending it, --creation-tx to help the creation match, --sourcify-url to target another server, and -o to keep the rewritten source.

Note: creation matches are only guaranteed when __init__ calls ≤1 internal function; the init-callee section of creation code is not forced by source order. Runtime matches are always forceable.

Match without submitting

To recover the layout and prove the match locally — against on-chain code or a hex file — without involving a verifier:

vysort match contract.vy --address 0x2cced4ff... --rpc-url https://eth.drpc.org -o matched.vy
vysort match contract.vy --runtime runtime.hex -o matched.vy

The deployed layout is recovered in 2 compiles regardless of contract size: one instrumented compile maps each internal function's section boundaries and masks the layout-dependent address bytes, the deployed order is then decoded straight off the on-chain bytes, and one reordered stock compile verifies it byte-exactly — exact, or prefix when the deployed code carries an appended immutable tail. If the decode hits an edge case, reachable layouts are brute-forced one compile at a time as a fallback. For unaffected compiler versions a single compile-and-compare runs instead. --evm-version istanbul helps pre-berlin deployments whose nonreentrant lock constants differ.

The matched source written by -o is ordinary vyper that any stock compiler of that version turns into the deployed bytecode — auxdata contains no source hash, so the output is byte-identical to what the original source produces under that ordering.

Developer curiosities

The remaining subcommands expose the machinery.

Analyze a contract for ordering nondeterminism:

vysort check contract.vy

{
  "internal_fns": 2,
  "decision_points": 1,
  "reachable_layouts": 2,
  "immune": false,
  "env_layout": ["_triple", "_double"],
  "layouts": [["_double", "_triple"], ["_triple", "_double"]]
}

immune: true means exactly one layout is reachable — the contract was never at risk; this covers 93% of affected-band mainnet contracts. Otherwise layouts (when small) enumerates every layout the deployer's heap could have produced. The check is version-aware: sources targeting compilers outside the affected 0.3.4–0.3.7 band short-circuit to immune: true without compiling.

Force an arbitrary layout by rewriting the source:

vysort reorder contract.vy _double,_triple -o forced.vy
vysort reorder contract.vy layout.json > forced.vy

The layout is a comma-separated list of internal function names or a JSON file (["_double", "_triple"]). This is the forcing primitive match and verify are built on.