adopt-c-bounds-safety

name	adopt-c-bounds-safety
description	Guide for the C -fbounds-safety language extension. Covers the language model, pointer annotations, adopting bounds-safety in existing C code, compiler build settings and modes, and runtime debugging of bounds violations.
when_to_use	When working with, reading, reviewing, comparing, debugging or analyzing C code that has adopted -fbounds-safety or wants to adopt it. Key syntax to look for Bounds annotations (__counted_by, __counted_by_or_null, __sized_by, __sized_by_or_null, __ended_by, __single, __indexable, __bidi_indexable, __unsafe_indexable, __null_terminated, __terminated_by), its helper functions (e.g.: __unsafe_forge_bidi_indexable, __unsafe_forge_single, __null_terminated_to_indexable, __unsafe_null_terminated_to_indexable, __unsafe_null_terminated_from_indexable) or other macros (e.g. __ptrcheck_abi_assume_single) or includes of "ptrcheck.h".
effort	high

How to Use This Skill

When helping with -fbounds-safety adoption or code changes, ask clarifying questions about the user's codebase and goals before suggesting changes. For complex tasks involving multiple files or non-trivial annotation decisions, use plan mode to propose an approach before implementing.

-fbounds-safety Language Extension

-fbounds-safety is a C language extension that prevents out-of-bounds memory access by enforcing bounds safety at the language level. It inserts automatic bounds checks at runtime, rejects unsafe pointer operations at compile time, and requires programmers to provide bounds annotations so the compiler can guarantee safety. Out-of-bounds accesses become deterministic traps instead of exploitable vulnerabilities.