tm_cvmx_set(9)

📦 version 7.3.1, in nixpkgs unstable

💅 tm_cvmx_set(9) 💅

okay so this is a page from the Kernel API Manual — yes, section 9, the big-kid kernel one — and it's all about tm_cvmx_set. bestie, we're going in 🫶

✨ NAME ✨

tm_cvmx_set — set CMVX registers. that's it, that's the whole vibe check. setting registers. slay 👑

🌸 SYNOPSIS 🌸

int tm_cvmx_set (struct task_struct *target , const struct user_regset
*regset , unsigned int pos , unsigned int count , const void *kbuf ,
const void __user *ubuf );

like, five whole arguments, and she returns an int. no cap, she's booked and busy 💅

🎀 ARGUMENTS 🎀

  • target — the target task. the actual lil thread/task we're messing with, main character energy tbh.
  • regset — the user regset structure. this is the regset handle for the user side of things 🦋
  • pos — the buffer position. where in the buffer we're starting, iykyk.
  • count — number of bytes to copy. exactly how many bytes, no more no less, periodt.
  • kbuf — kernel buffer to copy into. that's the destination, remember it 💖
  • ubuf — user buffer to copy from. that's the source. user memory, so, you know, careful 🙈

🦋 DESCRIPTION 🦋

so what does she do? this function sets in transaction checkpointed VMX registers. literally that. the checkpointed VMX registers get set, because that's her job and she ate 🔥

now the important bit, bestie, pay attention: when the transaction is active, ckvr_state and ckvrsave hold the checkpointed values for the current transaction — the ones it falls back on if it aborts in between. like a save point in a game, except it's registers and the stakes are higher 😭

the userspace interface buffer layout is, and I quote (well, I quote the layout, it's facts not vibes):

struct data {
        vector128       vr[32];
        vector128       vscr;
        vector128       vrsave;
};

that's the whole struct. vr[32], plus vscr, plus vrsave. all vector128. iconic ✨

💜 SEE ALSO 💜

kernel file ./arch/powerpc/kernel/ptrace/ptrace-tm.c — the whole tm fam, and honestly they're all worth a read:

ngl this one's short but she's dense. everything here is facts, so don't come for me if you skimmed it 🌈

and that's the page!! mwah 💋 this lil gem lives in ./arch/powerpc/kernel/ptrace and the date stamp says October 2026 — so yeah, from the future, obviously 🧚⭐💜

📦 where this page comes from