### What does this PR do?
- **Use `Latin1Character` instead of `LChar`**
- **Fix for
0875bc8f62**
### How did you verify your code works?
---
# WebKit Update Summary (September 2025)
## Overview
This document summarizes the major changes in WebKit/JavaScriptCore from
the September 2025 update. The update includes approximately 254
JSC-related commits with significant improvements to performance,
stability, and developer experience.
## Critical Bug Fixes
### Memory Safety
- **operationMaterializeObjectInOSR fix** (5c7aadfa0a96): Fixed
uninitialized Butterfly storage during OSR exits with sunk Array
allocations. This prevents potential crashes when arrays with holes are
materialized during OSR exit.
- **FTL materialization fixes** (a72d19840714, ed1e6fe03899): Added
missing internal object type handling in FTL materialization, improving
stability during optimization bailouts.
### Promise and Async Improvements
- **JSPromiseReaction object** (a1cb5e087a46, later reverted in
b0566a4db201): Initially introduced to improve promise reaction handling
but was reverted due to compatibility issues with Bun's modifications.
- **Async stack traces enhancements**:
- Added support for `Promise.any` in async stack traces (d9a997b3edaa)
- Added empty JSValue checking for async stack trace safety
(9d26223d4bcb)
- Promise.all support was added and later reverted due to performance
concerns
## Performance Optimizations
### JIT Compiler Improvements
- **B3 Immutable Loads** (570a3530f949, 62300f8db3d9): Added
immutability annotations and CSE optimizations for loads that can look
for targets in dominators
- **BBQ JIT enhancements**:
- Fixed callee-save register handling (c7ae05719045)
- Simplified F32 copysign operations (e0651af57025)
- **DFG optimizations**:
- Fixed RegExp constant folding with materialized NewRegExp nodes
(7b53a04a5afa)
- Improved RegExp object node handling in strength reduction
(eeb65e05095b)
### WebAssembly Improvements
- **WASM SIMD Support**:
- Added v128 support for IPInt call and tail-call instructions
(73f0c9d430cb)
- Implemented v128 support in local.get, local.set, global.get,
global.set (67d7bf15139a)
- Added x86_64 SIMD integer arithmetic and float instructions
- **WASM Memory Management**:
- Introduced WasmInstanceAnchor for better instance lifecycle management
(f9f1ed183bf7)
- Attached AbstractHeap to wasm memory access for better optimization
(f183c6f7def4)
- Added signal handling for null checks in wasm (bf18b5b709f3)
- **WASM Debugging**: Added LLDB debugging infrastructure for
WebAssembly (e03c10225cc8)
## API and Language Features
### Iterator Helpers
- Merged `Iterator.prototype.sliding` into `Iterator.prototype.windows`
(1d49e823702d)
- Optimized iterator next method calls using CachedCall (5ee92514060c)
### Math Extensions
- Improved performance of `Math.sumPrecise` implementation
(602294057337)
### Error Handling
- Enhanced error messages for for-of loops without Symbol.iterator
(0051bbf2491f)
## Infrastructure Changes
### Character Type Refactoring
- **LChar to Latin1Character rename** (63b97b511366, 1424f0687876):
Major refactoring replacing the `LChar` type with `Latin1Character`
throughout the codebase for better clarity
- Additional fixes for Latin1Character usage (711eab3243f0,
50bf8e6fd4ca, 88e29ab76aec)
### Build System
- Fixed builds with GCC 15.x (e33b18bc59d6)
- Added gitattributes for JSC test files (82c4cc796da6)
- Improved test runner with comprehensive verbose logging (7ef95c177a42)
- Added memory-limited annotations for tests using excessive memory
(b991cd17d612)
### Testing Infrastructure
- Improved handling of missing test executables (db1e3bbb3be2)
- Added support for non-customized ICU 74.2 in intl tests (c922a28b6642)
- Fixed various test configuration issues and timeouts
## Bun-Specific Modifications
### Preserved Customizations
- Maintained `BUN_JSC_ADDITIONS` for Bun-specific features
- Kept async context support for AsyncLocalStorage
- Preserved V8 heap snapshot compatibility layer
- Maintained custom inspector extensions
### Conflicts Resolved
- Successfully merged upstream changes while preserving Bun's event loop
integration
- Resolved conflicts in promise handling while maintaining Bun's async
behavior
- Fixed re-declaration issues with `isAsyncFrame` for async stack traces
## Breaking Changes and Reverts
### Reverted Features
1. **JSPromiseReaction object**: Reverted due to conflicts with Bun's
promise handling
2. **Promise.all async stack trace support**: Reverted due to ~4%
performance regression in JetStream3/doxbee-async benchmark
3. **Array.prototype.flat C++ implementation**: Reverted (reason not
specified in commit)
## Security Improvements
- Type safety improvements with uncheckedDowncast for Wasm::Callee
(48425afd643d)
- Added bounds checking and validation for Wasm array operations
(b5148db1c4c1)
- Improved memory safety with proper initialization of materialized
objects
## Platform Support
- macOS: Continued support for x64/arm64
- Linux: Maintained glibc/musl compatibility
- Windows: Preserved x64 support
- Fixed platform-specific alignment issues for x86_64 (94a60eb123c5)
## Notable Debugging Enhancements
- LLDB infrastructure for WebAssembly debugging
- Improved verbose command logging in test runners
- Enhanced stack trace capabilities for async functions
- Better error reporting for missing Symbol.iterator
## Performance Metrics
- Several memory optimizations for test execution
- JIT memory reservation size adjustments for debug builds
- Optimized iterator operations with cached calls
- Improved Math.sumPrecise performance
## Future Considerations
- The JSPromiseReaction implementation may need revisiting with adjusted
architecture
- Async stack trace support for Promise.all requires performance
optimization
- Continued work on WASM SIMD support for additional operations
## Migration Notes for Bun Team
1. **LChar usage**: All references to `LChar` have been replaced with
`Latin1Character`
2. **Promise handling**: The reverted JSPromiseReaction changes indicate
potential architectural conflicts that may need addressing
3. **Test configuration**: New memory-limited annotations should be used
for memory-intensive tests
4. **Build flags**: Ensure USE_BUN_JSC_ADDITIONS and USE_BUN_EVENT_LOOP
remain enabled
### What does this PR do?
### How did you verify your code works?
---------
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
### What does this PR do?
Evidently, Ubuntu turns them on by default.
Claude:
```
> What is the typical overhead for glibcxx assertions?
⏺ The overhead of glibc/libstdc++ assertions can be significant, especially in
performance-critical code:
Typical Overhead Ranges:
libstdc++ (C++ standard library) assertions:
- 5-15% overall performance impact in typical applications
- Up to 30-50% in container-heavy code (vectors, maps, etc.)
- Iterator validity checks are particularly expensive
glibc (C library) assertions:
- 2-8% overall impact in typical applications
- Up to 20% in malloc/free intensive code
- Heap consistency checks, buffer overflow detection
```
### What does this PR do?
Enables async stack traces
### How did you verify your code works?
Added tests
---------
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
### What does this PR do?
### How did you verify your code works?
---------
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
### What does this PR do?
### How did you verify your code works?
---------
Co-authored-by: Jarred-Sumner <709451+Jarred-Sumner@users.noreply.github.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
## Summary
- Updates WebKit commit from `684d4551ce5f62683476409d7402424e0f6eafb5`
to `aa4997abc9126f5a7557c9ecb7e8104779d87ec4`
- Build completed successfully with no errors
- Verified functionality with hello world test
## Test plan
- [x] Build completed successfully
- [x] Hello world test passes with `bun bd`
- [x] No build errors encountered
🤖 Generated with [Claude Code](https://claude.ai/code)
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
## Summary
- Updates WebKit from 75f6499 to eb92990 (latest release from
oven-sh/webkit)
- This brings in the latest WebKit improvements and fixes
## Test plan
- [ ] Verify the build completes successfully
- [ ] Run existing test suite to ensure no regressions
🤖 Generated with [Claude Code](https://claude.ai/code)
---------
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
### What does this PR do?
<!-- **Please explain what your changes do**, example: -->
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### How did you verify your code works?
ran fuzzy-wuzzy.test.ts
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- [ ] JSValue used outside of the stack is either wrapped in a
JSC.Strong or is JSValueProtect'ed
- [ ] I wrote TypeScript/JavaScript tests and they pass locally
(`bun-debug test test-file-name.test`)
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