Prompt file imported from xsscx/xnuimagetools (.github/prompts/code-review.prompt.md). Copyright stays with the author.

Code Review — XNU Image Tools

Review all sub-projects for bugs, memory safety issues, build correctness, and opportunities to improve fuzzing coverage.

Sub-Projects to Review

1. VideoToolbox Fuzzer (Critical — C/ObjC, manual memory)

Files: VideoToolbox/Fuzzing/videotoolbox-runner.m, videotoolbox-interposer.c, runner.c, runner_dist.c, interpose.c

Checklist

• All malloc() / calloc() returns checked for NULL
• All CVPixelBufferLockBaseAddress paired with Unlock
• All CMSampleBufferRef released with CFRelease
• All CVImageBufferRef properly retained/released
• AVAssetReader error handling complete
• CIContext and CGColorSpace properly released in save_fuzzed_frame()
• No buffer overflows in fuzzing mutation code
• timeout handling — clean exit on SIGALRM
• CLI argument parsing handles edge cases (-t 0, -t negative, missing file)

2. iOS Fuzzer (ObjC, shared with xnuimagefuzzer)

Files: XNU Image Fuzzer/XNU Image Fuzzer/xnuimagefuzzer.m

Checklist

• All 17 bitmap context functions have NULL checks
• Memory released on all error paths
• CGBitmapInfo uses explicit casts from CGImageAlphaInfo
• No duplicate #define macros
• Buffer sizes correct for each pixel format depth
• DisplayP3 / BT2020 paths follow the same cleanup and ICC-save rules as legacy contexts

3. iOS Image Generator (Swift)

Files: XNU Image Generator for iOS/.../ContentView.swift

Checklist

• Image save operations handle errors
• File paths properly constructed
• No force-unwrapping of optionals
• Memory pressure handled for large image generation

4. Watch App (Swift)

Files: XNU Image Generator for Watch/.../ContentView.swift

Checklist

• Memory constraints respected (watchOS has limited RAM)
• Image sizes appropriate for watch display
• Sharing via Transferable protocol works correctly

Build Verification

Required Framework Links (VideoToolbox)

The videotoolbox-runner MUST link ALL of these:

-framework VideoToolbox
-framework Foundation
-framework AVFoundation
-framework CoreFoundation
-framework CoreMedia
-framework CoreVideo
-framework CoreImage
-framework CoreGraphics  ← CRITICAL: needed for save_fuzzed_frame()
-framework ImageIO
-framework UniformTypeIdentifiers
-lz

Makefile Targets

Verify the Makefile builds all targets without errors:

cd VideoToolbox/Fuzzing && make clean && make all

Check iOS targets separately (require iphoneos SDK):

make videotoolbox-interposer-arm64e.dylib
make videotoolbox-runner.app

Common Bug Patterns

VideoToolbox

// BAD: CVPixelBuffer lock without unlock on error
CVPixelBufferLockBaseAddress(pixelBuffer, 0);
if (error) return;  // Leaked lock!

// GOOD: Always unlock
CVPixelBufferLockBaseAddress(pixelBuffer, 0);
if (error) {
    CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);
    return;
}
// ... use pixel buffer ...
CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);

CoreGraphics

// BAD: Missing CoreGraphics framework link
CGColorSpaceRef cs = CGColorSpaceCreateDeviceRGB();  // Linker error!

// GOOD: Ensure -framework CoreGraphics in build command

Build System

# BAD: Duplicate framework
-framework VideoToolbox -framework VideoToolbox

# GOOD: Each framework listed once
-framework VideoToolbox