PR_SET_TSC(2const)

💅 PR_SET_TSC (the 2const one, bestie)

okay so you know how prctl(2) has like a million little sub-commands and you're supposed to just know which one does what? yeah. this is one of them. it lives in the 2const corner of the manual, and honestly? she's a lil niche x86 queen. 🎀

It's all about the timestamp counter — that RDTSC-ish thing your CPU keeps ticking away — and whether your process is allowed to read it. That's it. That's the whole job. 👑

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✨ NAME ✨

PR_SET_TSC — change whether the timestamp counter can be read by the process

yes literally that. no cap. 🦋

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📚 LIBRARY 📚

Standard C library (libc, -lc)

like every other normal human function, she's just chillin' in libc. 🫶

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🌸 SYNOPSIS 🌸

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

int prctl(PR_SET_TSC, long flag);

so you're calling prctl (the big grab-bag syscall wrapper) and you're passing PR_SET_TSC as the operation, plus one long called flag. That flag is where you tell her what vibe you want. 💫

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💖 DESCRIPTION 💖

So what she does is: she sets the state of the flag that determines whether the timestamp counter can be read by the process. Think of it like a lil permission switch on your process, and the CPU's counter is the thing behind it. 🎀

And you flip that switch with flag, and there are exactly two moods:

• PR_TSC_ENABLE — pass this and you're allowing the timestamp counter to be read. she's unlocked. go read it. ✨
• PR_TSC_SIGSEGV — pass this and the process gets hit with a SIGSEGV the moment it tries to read the timestamp counter. not a fun surprise. she said no. 💀

fr fr, that second one is not a gentle "permission denied" — it's a whole signal. so if you hand PR_TSC_SIGSEGV to some code that's just casually reading the TSC, you're gonna have a bad time. 😭

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🔥 RETURN VALUE 🔥

• On success: 0 is returned. slay. ✅
• On error: -1 is returned, and errno gets set to tell you what went wrong. 🙈

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👑 ERRORS 👑

• EINVAL — flag is not a valid value.

that's it. that's the only one on the list. give her a flag she doesn't recognise and she simply Will Not. 💅

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🌈 STANDARDS 🌈

• Linux.
• x86 only.

so if you're out here on some other architecture, bestie, this is not the page for you. x86 girlies only. 🧚

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⭐ HISTORY ⭐

• Linux 2.6.26 (x86).

ancient by now but still iconic. 👑

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🦋 SEE ALSO 🦋

• prctl(2)
• PR_GET_TSC(2const)

(that second one is the read-only sibling — she asks, this one tells. iykyk. 💜)

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that's the whole page, every single detail intact, nothing skipped, she's fully unhinged but 100% accurate. 🎀

smooches, and remember: read your man pages, check your errno, and never hand PR_TSC_SIGSEGV to a process that's just vibing. 💅✨

this lil love letter is from Linux man-pages 6.20, dated 2026-02-08 — mwah, bye bestie! 🫶🌸