GCC 16 guarantees trampoline-free nested functions and GCC 17 merges builtins that extend it to captures

Sources: Martin Uecker, 2026-07-14, HN discussion
Summary: Taking the address of a nested function historically forced an executable stack or a heap allocation that could leak across longjmp. GCC 16 guarantees the trampoline-free form, and GCC 17 merges __builtin_call_code_address and __builtin_call_static_chain, which extend the guarantee to captures while keeping access to the parent frame.
Why it matters: C code that used nested functions can drop the executable-stack requirement that hardened toolchains and kernels reject.