__flex_counter(9)

💅 __flex_counter 💅

okay so this is a kernel API manual page, from the <pink>Kernel API Manual</pink> girlies, and today's main character is __flex_counter — the little helper that grabs you a pointer to the counter member of a flexible array, but only if somebody was cute enough to annotate it with __counted_by(). iykyk 🎀

---

✨ NAME ✨

__flex_counter — get a pointer to the counter member of the given flexible array, if it was annotated with __counted_by() 🌸

✨ SYNOPSIS ✨

__flex_counter (FAM );

✨ ARGUMENTS ✨

• FAM — pointer to the flexible array member of an addressable struct instance, bestie. that's the whole vibe. 🦋

✨ DESCRIPTION ✨

okay so picture this, right? you've got something like:

struct foo { int counter; short array[] __counted_by(counter); } *p;

and then __flex_counter(p->array) will literally resolve to p->counter. slay. it's giving "find the counter, no cap." 👑

⚠️ heads up though: Clang may not allow this to be assigned to a separate variable — it must be used directly. not me finding that out the hard way 😭 so don't try to stash it in a local and go about your day, fr fr.

and if p->array is unannotated? it returns (void *)NULL. that's it. that's the whole story. 💀 no annotation, no counter, no nothing. vibe check failed, respectfully. 🙈

✨ SEE ALSO ✨

• Kernel file ./include/linux/compiler_types.h
• compiletime_assert(9) ⭐

---

and that's the page, bestie! 🫶 this one lives in ./include/linux, dated October 2026 — mwah, go annotate your flexible arrays, ily 💖🧚✨