jr_func(9)

📦 version 7.3.1, in nixpkgs unstable

💅 jr_func 💅

okay so bestie, welcome to the jr_func(9) page — that's section 9 of the Kernel API Manual, aka the kernel-functions zone, aka where the MIPS emulation girlies live 🦋

✨ NAME ✨

jr_func — literally emulates a JR instruction. that's the whole vibe. no cap 🎀

🌸 SYNOPSIS 🌸

int jr_func (struct pt_regs *regs , u32 ir );

🧚 ARGUMENTS 🧚

  • regs — bestie… the docs say -- undescribed -- 😭 like they really just left her hanging. she's a struct pt_regs * and that's all we're getting, iykyk.
  • ir — the Instruction, as a u32. the actual instruction, the moment, the main character 👑

💖 DESCRIPTION 💖

so what does it return? glad you asked, because it's giving very choose-your-own-adventure 🌈 here's the whole roster:

  • SIGILL — if JR was in the delay slot 🙈 like ma'am, that's illegal, that's the whole point of SIGILL.
  • SIGEMT — if we can't compute the EPC. we tried, we literally tried 😭
  • SIGSEGV — if we can't access the userland instruction. access denied bestie, memory said no 💀
  • 0 — success! slay! iconic! periodt ✨👑

🔥 SEE ALSO 🔥

first up, the kernel file herself: ./arch/mips/kernel/mips-r2-to-r6-emul.c — yes that's the file, yes you should look at it 🫶

and the whole emulation friend group, all of them, no one left out:

okay that's the page!! huge thank you to ./arch/mips/kernel for the source, and to October 2026 for the date — mwah, love you, bye bestie 💜🎀✨

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