_cpacf_kmac(9)

📦 version 7.3.1, in nixpkgs unstable

🌸 _cpacf_kmac — NAME ✨

okay so bestie, meet _cpacf_kmac 💅 — literally the function that executes the KMAC (COMPUTE MESSAGE AUTHENTICATION CODE) instruction and updates the flags in gr0. that's her whole job. iconic behavior, no notes 🎀

this is from the Kernel API Manual, iykyk 🦋

✨ SYNOPSIS ✨

int _cpacf_kmac (unsigned long *gr0 , void *param , const u8 *src , long
src_len );

like, that's the whole signature bestie, she's not complicated 🫶

🎀 ARGUMENTS 🎀

  • gr0 — a pointer to gr0 (that's the fc and flags btw) that gets passed to KMAC 💖 go check the CPACF_KMAC_xxx defines, they're right there
  • param — the address of the parameter block 🌸 see POP for the deets on each func, it's giving reference-material main character energy
  • src — the address of the source memory area 🦋 that's where the data lives
  • src_len — the length of the src operand, in bytes ✨ yes, bytes, keep up

💜 DESCRIPTION 💜

so what does she return? slay, here it is:

  • returns 0 for the query func 👑
  • returns the number of processed bytes for digest funcs 🍓

that's it. that's the vibe check. periodt 💅

🌈 SEE ALSO 🌈

okay so the kernel file to go look at is ./arch/s390/include/asm/cpacf.h — and then the whole friend group of related pages, all of them, no cap:

fr fr go read them all, they're lowkey obsessed with each other 🫶

and that's the page bestie!! 💖 this little gem lives over at ./arch/s390/include/asm, dated October 2026 ⭐, and she answers to _cpacf_kmac(9) — ok bye, go write some kernel code, ily 😭💅

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