PR_GET_TID_ADDRESS(2const)

💖 PR_GET_TID_ADDRESS 💖

okay bestie, welcome to PR_GET_TID_ADDRESS(2const) — yes that's the manual name, it's giving "const page" energy, and we're about to get into the clear_child_tid address situation. buckle up 🎀

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✨ NAME ✨

PR_GET_TID_ADDRESS — get the clear_child_tid address 🧚

📚 LIBRARY 📚

Standard C library (libc, -lc)

🌸 SYNOPSIS 🌸

#include <linux/prctl.h>  /* Definition of PR_* constants */
#include <sys/prctl.h>

int prctl(PR_GET_TID_ADDRESS, int **addrp);

👑 DESCRIPTION 👑

so like. this returns the clear_child_tid address — the one that got set by set_tid_address(2) and the clone(2) CLONE_CHILD_CLEARTID flag — and it drops it right into the location that addrp points to. 💅

heads up bestie: this feature is ONLY available if the kernel was built with the CONFIG_CHECKPOINT_RESTORE option enabled. no config, no vibes. 😭

🔥 RETURN VALUE 🔥

• On success, 0 is returned. slay ✨
• On error, -1 is returned, and errno is set to indicate the error. tragic 💀

💀 ERRORS 💀

• EFAULT — addrp is an invalid address. not her finest moment 🙈

🌈 STANDARDS 🌈

Linux.

🦋 HISTORY 🦋

Linux 3.5. old money, lowkey iconic ⭐

⚠️ CAVEATS ⚠️

okay so pay attention here because this one is a whole thing. since the prctl() system call does not have a compat implementation for the AMD64 x32 and MIPS n32 ABIs, and the kernel writes out a pointer using the kernel's pointer size, this operation expects a user-space buffer of 8 (not 4) bytes on these ABIs. yes. eight. not four. do not come to me with four bytes on those ABIs, I will know. 💅

🔗 SEE ALSO 🔗

• prctl(2)

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and that's the whole page bestie, no cap, every flag and caveat accounted for 🫶

this little adventure was brought to you by Linux man-pages 6.20, dated 2026-02-08, and the letters PR_GET_TID_ADDRESS(2const). mwah 💖✨