futex_syscall(9)

🦋 futex_syscall(9) — the Kernel API Manual, bestie edition 🦋

okay so this is a page from the Kernel API Manual and it's literally about futex_syscall, which is the wrapper around the SYS_futex syscall. buckle up, we're going in 💅

---

🌸 NAME 🌸

futex_syscall — the SYS_futex syscall wrapper. yes that's it. that's the whole name section. iconic brevity.

---

✨ SYNOPSIS ✨

int futex_syscall (volatile u_int32_t *uaddr , int op , u_int32_t val ,
struct timespec *timeout , volatile u_int32_t *uaddr2 , int val3 , int
opflags );

seven arguments. seven. she's high-maintenance but she delivers 🫶

---

🎀 ARGUMENTS 🎀

• uaddr — the address of the first futex. that's her home base 💖
• op — the futex op code. which move are we doing, queen?
• val — typically the expected value sitting at uaddr, but ngl it varies by op. so don't come for me if it's something else
• timeout — usually an absolute struct timespec (except where it says otherwise!!). some ops straight-up overload this one, so read the fine print 🙈
• uaddr2 — the address of the second futex, for the ops that need two. yes, some of them are that extra
• val3 — varies by op. mystery queen. we love a flexible parameter ✨
• opflags — flags you bitwise OR into op, like FUTEX_PRIVATE_FLAG. OR them in, bestie, that's the whole vibe 🔥

---

💜 DESCRIPTION 💜

futex_syscall is used by all of the following futex op wrappers. all of them. she's the main character and everyone else is her supporting cast 👑

she can also be used for misuse and abuse testing 😭 like, go off, but you were warned. generally though? use the specific op wrappers instead. they're the well-behaved ones and honestly you'll have a better time.

these argument descriptions are the defaults for all the like-named arguments in the following wrappers — except where noted below. so if something says otherwise down the page, that note wins. periodt. 💅

no cap: this page is literally the reference for the arguments of every wrapper that follows, so keep it open in another tab. you'll thank me later 🫶

---

🌈 SEE ALSO 🌈

• the kernel file ./tools/perf/bench/futex.h 👀
• futex_wait(9)
• futex_wake(9)
• futex_lock_pi(9)
• futex_unlock_pi(9)
• futex_cmp_requeue(9)
• futex_wait_requeue_pi(9)
• futex_cmp_requeue_pi(9)

that's the whole friend group right there. say hi to all of them for me 💖

---

and that's the page!! mwah 💋 this little gem lives in ./tools/perf/bench and she's dated October 2026 — mark your calendars, bestie, she's a whole era ⭐🧚‍♀️🍓