facebook/fishhook

Health v2 · maintenance only

Flags: no_releases

Adoption not part of the score

5425 stars · 988 forks observed · 2026-08-28

What it is AI-extracted, prompt v1, taxonomy v1, 2026-08-29, confidence not recorded

fishhook is a small C library from Facebook that dynamically rebinds symbols in Mach-O binaries running on iOS, similar to DYLD_INTERPOSE on macOS. It works by rewriting the lazy and non-lazy symbol pointer sections of the __DATA segment, letting you intercept calls to system library functions.

Use cases

• hook system library calls in an iOS app for debugging
• trace file descriptor close calls to find double-close bugs
• intercept C functions like open and close at runtime on iOS
• rebind symbols in a Mach-O binary without DYLD_INTERPOSE
• instrument libSystem calls during iOS development

When to choose

• you need to intercept calls to libSystem or other C functions on iOS in the simulator or on device
• you want a tiny, dependency-free C library you can drop into an Xcode project
• you need DYLD_INTERPOSE-like behavior inside an iOS app where dyld environment variables aren't available

When to avoid

• you need to hook Objective-C or Swift methods rather than C symbols - use method swizzling instead
• you target Android, Linux, or other non-Mach-O platforms
• you need to hook statically linked symbols or functions bound outside __la_symbol_ptr/__nl_symbol_ptr sections

Facets

library · maturity maintenance

security developer-tools apple-ecosystem developer-tools reverse-engineering cpp mach-o symbol-rebinding dyld hooking objective-c mobile-development debugging ios macos

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markdown · JSON · MCP: product_card(name="facebook/fishhook")