fix(compile): use 8-byte header for embedded section to ensure bytecode alignment #25377

dylan-conway · 2025-12-06T19:54:12Z

Summary

Change the size header in embedded Mach-O and PE sections from u32 (4 bytes) to u64 (8 bytes)
Ensures the data payload starts at an 8-byte aligned offset, which is required for the bytecode cache

Test plan

Test standalone compilation on macOS
Test standalone compilation on Windows

🤖 Generated with Claude Code

…de alignment Change the size header in embedded Mach-O and PE sections from u32 (4 bytes) to u64 (8 bytes). This ensures the data payload starts at an 8-byte aligned offset, which is required for the bytecode cache. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <[email protected]>

robobun · 2025-12-06T19:54:21Z

^{Updated 2:19 PM PT - Dec 6th, 2025}

❌ @dylan-conway, your commit 9e578ff has 4 failures in Build #32961 (All Failures):

test/v8/v8.test.ts - 1 failing on 🐧 13 x64-asan
test/js/node/test/parallel/test-http-exceptions.js - crash reported on 🐧 13 x64-asan
test/js/node/test/parallel/test-fs-readdir-stack-overflow.js - timeout on 🍎 13 aarch64
test/integration/next-pages/test/dev-server.test.ts - 1 failing on 🍎 13 aarch64

🧪 To try this PR locally:

bunx bun-pr 25377

That installs a local version of the PR into your bun-25377 executable, so you can run:

bun-25377 --bun

coderabbitai · 2025-12-06T19:57:14Z

Walkthrough

Standalone module graph Mach-O and PE length fields and headers were widened from 32-bit to 64-bit. Size/type changes propagate to accessor signatures, on-disk header offsets (data now starts after an 8-byte header), padding/offset calculations, and a new PE data accessor was added.

Changes

Cohort / File(s)	Summary
Mach-O format & accessors `src/StandaloneModuleGraph.zig`, `src/bun.js/bindings/c-bindings.cpp`, `src/macho.zig`	Blob header size field changed u32 → u64. Mach-O length accessor signature changed to return an optional u64. Header size increased from 4 to 8 bytes; data offsets, padding, and writes/reads adjusted to use 8-byte header semantics.
PE format & accessors `src/StandaloneModuleGraph.zig`, `src/bun.js/bindings/c-bindings.cpp`, `src/pe.zig`, `test/regression/issue/pe-codesigning-integrity.test.ts`	PE Bun-section length handling changed from 32-bit to 64-bit: accessor signatures now return u64, on-disk length prefix is 8-byte LE, data offsets adjusted to skip 8 bytes, boundary/overflow checks widened for 64-bit. Added `Bun__getStandaloneModuleGraphPEData()` to expose PE section data pointer. Test updated to expect 8-byte size header.

Possibly related PRs

feat(windows): implement authenticode stripping for --compile #22960: Changes the same PE/Mach-O section length fields, BlobHeader layout, and related accessors as part of the 32-bit→64-bit length migration.

Pre-merge checks

❌ Failed checks (1 inconclusive)

Check name	Status	Explanation	Resolution
Description check	❓ Inconclusive	The description covers the main change and test plan but does not follow the repository's required template structure with explicit 'What does this PR do?' and 'How did you verify your code works?' sections.	Restructure the description to follow the template with clear sections for 'What does this PR do?' and 'How did you verify your code works?' to ensure consistency with repository standards.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and specifically describes the main change: switching to an 8-byte header for embedded sections to achieve bytecode alignment.

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📥 Commits

Reviewing files that changed from the base of the PR and between 457ab88 and 9e578ff.

📒 Files selected for processing (1)

test/regression/issue/pe-codesigning-integrity.test.ts (2 hunks)

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📓 Path-based instructions (4)

test/**/*.{js,ts,jsx,tsx}

📄 CodeRabbit inference engine (.cursor/rules/writing-tests.mdc)

test/**/*.{js,ts,jsx,tsx}: Write tests as JavaScript and TypeScript files using Jest-style APIs (test, describe, expect) and import from bun:test
Use test.each and data-driven tests to reduce boilerplate when testing multiple similar cases

Files:

test/regression/issue/pe-codesigning-integrity.test.ts

test/**/*.test.{ts,js,jsx,tsx,mjs,cjs}

📄 CodeRabbit inference engine (test/CLAUDE.md)

test/**/*.test.{ts,js,jsx,tsx,mjs,cjs}: Use bun:test with files that end in *.test.{ts,js,jsx,tsx,mjs,cjs}
Do not write flaky tests. Never wait for time to pass in tests; always wait for the condition to be met instead of using an arbitrary amount of time
Never use hardcoded port numbers in tests. Always use port: 0 to get a random port
Prefer concurrent tests over sequential tests using test.concurrent or describe.concurrent when multiple tests spawn processes or write files, unless it's very difficult to make them concurrent
When spawning Bun processes in tests, use bunExe and bunEnv from harness to ensure the same build of Bun is used and debug logging is silenced
Use -e flag for single-file tests when spawning Bun processes
Use tempDir() from harness to create temporary directories with files for multi-file tests instead of creating files manually
Prefer async/await over callbacks in tests
When callbacks must be used and it's just a single callback, use Promise.withResolvers to create a promise that can be resolved or rejected from a callback
Do not set a timeout on tests. Bun already has timeouts
Use Buffer.alloc(count, fill).toString() instead of 'A'.repeat(count) to create repetitive strings in tests, as ''.repeat is very slow in debug JavaScriptCore builds
Use describe blocks for grouping related tests
Always use await using or using to ensure proper resource cleanup in tests for APIs like Bun.listen, Bun.connect, Bun.spawn, Bun.serve, etc
Always check exit codes and test error scenarios in error tests
Use describe.each() for parameterized tests
Use toMatchSnapshot() for snapshot testing
Use beforeAll(), afterEach(), beforeEach() for setup/teardown in tests
Track resources (servers, clients) in arrays for cleanup in afterEach()

Files:

test/regression/issue/pe-codesigning-integrity.test.ts

test/regression/issue/**/*.test.ts

📄 CodeRabbit inference engine (test/CLAUDE.md)

Regression tests for specific issues go in /test/regression/issue/${issueNumber}.test.ts. Do not put tests without issue numbers in the regression directory

Files:

test/regression/issue/pe-codesigning-integrity.test.ts

test/**/*.test.{ts,tsx}

📄 CodeRabbit inference engine (CLAUDE.md)

test/**/*.test.{ts,tsx}: For single-file tests in Bun test suite, prefer using -e flag over tempDir
For multi-file tests in Bun test suite, prefer using tempDir and Bun.spawn
Always use port: 0 when spawning servers in tests - do not hardcode ports or use custom random port functions
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Test files must end in .test.ts or .test.tsx and be created in the appropriate test folder structure

Files:

test/regression/issue/pe-codesigning-integrity.test.ts

🧠 Learnings (5)

📓 Common learnings

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/bun.js/bindings/v8/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:36:59.706Z
Learning: Applies to src/bun.js/bindings/v8/test/v8/v8.test.ts : Add corresponding test cases to test/v8/v8.test.ts using checkSameOutput() function to compare Node.js and Bun output

Learnt from: RiskyMH
Repo: oven-sh/bun PR: 24719
File: docs/bundler/executables.mdx:527-560
Timestamp: 2025-11-14T16:07:01.064Z
Learning: In the Bun repository, certain bundler features like compile with code splitting (--compile --splitting) are CLI-only and not supported in the Bun.build() JavaScript API. Tests for CLI-only features use backend: "cli" flag (e.g., test/bundler/bundler_compile_splitting.test.ts). The CompileBuildConfig interface correctly restricts these with splitting?: never;. When documenting CLI-only bundler features, add a note clarifying they're not available via the programmatic API.

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/registering-bun-modules.mdc:0-0
Timestamp: 2025-11-24T18:35:39.205Z
Learning: Add tests for new Bun runtime functionality

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-02T05:59:51.485Z
Learning: Applies to test/**/*.test.{ts,tsx} : Verify your test fails with `USE_SYSTEM_BUN=1 bun test <file>` and passes with `bun bd test <file>` - tests are not valid if they pass with `USE_SYSTEM_BUN=1`

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/bun.js/bindings/v8/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:36:59.706Z
Learning: Ensure V8 API tests compare identical C++ code output between Node.js and Bun through the test suite validation process

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : When spawning Bun processes in tests, use `bunExe` and `bunEnv` from `harness` to ensure the same build of Bun is used and debug logging is silenced

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/js/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:11.466Z
Learning: Write JS builtins for Bun's Node.js compatibility and APIs, and run `bun bd` after changes

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/js/node/test/{parallel,sequential}/*.js : For test/js/node/test/{parallel,sequential}/*.js files without a .test extension, use `bun bd <file>` instead of `bun bd test <file>` since these expect exit code 0 and don't use bun's test runner

Learnt from: RiskyMH
Repo: oven-sh/bun PR: 22606
File: src/glob/GlobWalker.zig:449-452
Timestamp: 2025-09-12T18:16:50.754Z
Learning: For Bun codebase: prefer using `std.fs.path.sep` over manual platform separator detection, and use `bun.strings.lastIndexOfChar` instead of `std.mem.lastIndexOfScalar` for string operations.

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/building-bun.mdc:0-0
Timestamp: 2025-11-24T18:34:55.173Z
Learning: Applies to src/**/*.{cpp,zig} : Run tests using `bun bd test <test-file>` with the debug build; never use `bun test` directly as it will not include your changes

📚 Learning: 2025-11-24T18:36:59.706Z

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/bun.js/bindings/v8/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:36:59.706Z
Learning: Applies to src/bun.js/bindings/v8/test/v8/v8.test.ts : Add corresponding test cases to test/v8/v8.test.ts using checkSameOutput() function to compare Node.js and Bun output

Applied to files:

test/regression/issue/pe-codesigning-integrity.test.ts

📚 Learning: 2025-10-03T18:29:20.173Z

Learnt from: alii
Repo: oven-sh/bun PR: 22504
File: src/bake/client/data-view.ts:4-4
Timestamp: 2025-10-03T18:29:20.173Z
Learning: In the Bun codebase, DataView<ArrayBuffer> is valid TypeScript syntax (supported since TypeScript 4.5+) and is used consistently across the bake client modules to provide type narrowing for DataView instances backed specifically by ArrayBuffer rather than SharedArrayBuffer.

Applied to files:

test/regression/issue/pe-codesigning-integrity.test.ts

📚 Learning: 2025-08-31T09:08:12.104Z

Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 22279
File: test/js/web/structured-clone-fastpath.test.ts:12-12
Timestamp: 2025-08-31T09:08:12.104Z
Learning: In Bun, process.memoryUsage.rss() is called as a direct function, not as process.memoryUsage().rss like in Node.js. This is the correct API shape for Bun.

Applied to files:

test/regression/issue/pe-codesigning-integrity.test.ts

📚 Learning: 2025-11-24T18:37:47.899Z

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/bun.js/bindings/v8/AGENTS.md:0-0
Timestamp: 2025-11-24T18:37:47.899Z
Learning: Applies to src/bun.js/bindings/v8/**/<UNKNOWN> : <UNKNOWN>

Applied to files:

test/regression/issue/pe-codesigning-integrity.test.ts

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

Update the PE codesigning integrity test to read the .bun section size as a u64 (8 bytes) instead of u32 (4 bytes), matching the format change in the previous commit. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <[email protected]>

github-actions bot added the claude label Dec 6, 2025

Jarred-Sumner merged commit 5eb2145 into main Dec 7, 2025
53 of 55 checks passed

Jarred-Sumner deleted the dylan/fix-bytecode-alignment-assertion branch December 7, 2025 00:37

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fix(compile): use 8-byte header for embedded section to ensure bytecode alignment #25377

fix(compile): use 8-byte header for embedded section to ensure bytecode alignment #25377

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fix(compile): use 8-byte header for embedded section to ensure bytecode alignment #25377

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