oven-sh/bun · error · Error

workload "${name}" wrote an invalid trace

Error message

workload "${name}" wrote an invalid trace

What it means

The trace file is large enough but its header magic/version words do not equal TRACE_MAGIC/1, so the file was not written by the current tracer. This guards against consuming stale or foreign data before trusting the address list.

Source

Thrown at scripts/orderfile/generate.ts:172

}

/** Write function starts for functrace.c: u64 magic, version, count, addresses. */
function writeStarts(path: string, addresses: number[]): void {
  const buffer = new ArrayBuffer((STARTS_HEADER_WORDS + addresses.length) * 8);
  const words = new BigUint64Array(buffer);
  words[0] = STARTS_MAGIC;
  words[1] = 1n;
  words[2] = BigInt(addresses.length);
  for (let i = 0; i < addresses.length; i++) words[STARTS_HEADER_WORDS + i] = BigInt(addresses[i]!);
  writeFileSync(path, new Uint8Array(buffer));
}

/** Read a trace functrace.c wrote: first-entry addresses, slide already removed. */
function readTrace(path: string, name: string): number[] {
  const raw = readFileSync(path);
  if (raw.byteLength < TRACE_HEADER_WORDS * 8) throw new Error(`workload "${name}" wrote a truncated trace`);
  const header = new BigUint64Array(raw.buffer, raw.byteOffset, TRACE_HEADER_WORDS);
  if (header[0] !== TRACE_MAGIC || header[1] !== 1n) throw new Error(`workload "${name}" wrote an invalid trace`);
  const count = Number(header[4]);
  if (count === 0) throw new Error(`workload "${name}" recorded no entries — is the tracer loading?`);
  const body = new BigUint64Array(raw.buffer, raw.byteOffset + TRACE_HEADER_WORDS * 8, count);
  const out: number[] = new Array(count);
  for (let i = 0; i < count; i++) out[i] = Number(body[i]);
  return out;
}

export function generateOrderFile(options: GenerateOptions): { count: number; outPath: string } {
  const buildDir = resolve(options.buildDir);
  const outPath = resolve(options.outPath ?? join(buildDir, "linker.order"));
  const minFunctions = options.minFunctions ?? MIN_FUNCTIONS;
  const log = (message: string) => options.verbose && console.log(message);

  const darwin = process.platform === "darwin";
  if (process.platform !== "linux" && !(darwin && process.arch === "arm64")) {
    throw new Error("the order file tracer builds on linux x86-64/arm64 or macOS arm64");
  }

View on GitHub (pinned to 8c5296ac45)

Solutions

1. Delete stale trace files / clear the output directory before re-running
2. Ensure each run uses a unique scratch out path (the generator already mkdtemp's its scratch)
3. Rebuild the tracer from the current functrace.c so writer and reader agree on the format

import { existsSync, unlinkSync } from "node:fs";

// A pre-existing out file may carry an older format — remove it so only the current tracer writes it.
if (existsSync(outPath)) unlinkSync(outPath);

try {
  processTrace(out);
} catch (err) {
  if (/invalid trace/.test(String(err))) {
    unlinkSync(out); // discard stale-format file
    return retryWorkload();
  }
  throw err;
}

When it happens

Trigger: A stale file already exists at the BUN_FUNCTRACE_OUT path from an earlier tracer revision; two tracer versions sharing an out path; a garbage/hand-made file left where the workload expects to write.

Common situations: Re-running generate with a reused out directory after functrace.c's format changed; concurrent runs writing to the same fixed path.

Related errors

• workload "${name}" wrote a truncated trace
• workload "${name}" recorded no entries — is the tracer loadi
• workload "${workload.name}" exited ${r.status} ${r.stderr}
• traced only ${order.length} functions, expected at least ${m
• ${options.label ?? cmd[0]}: ${r.error.message}

AI-assisted analysis of oven-sh/bun@8c5296ac45 (2026-08-16). Data as JSON: /api/errors/419bfe0a15ca38cd. Report an issue: GitHub.