__compute_r...epc_for_insn(9)

💅 __compute_r...epc_for_insn(9) — like, the Kernel API Manual girlies know ✨

okay so bestie, before we even start: yes, the title is literally abbreviated to __compute_r...epc_for_insn(9) and that's just how the Kernel API Manual rolls it. The full name is __compute_return_epc_for_insn and she is the main character here. No cap. 🎀

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🌸 NAME 🌸

__compute_return_epc_for_insn — computes the return address and does emulate branch simulation, if required. That's it, that's the vibe. 🦋

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⭐ SYNOPSIS ⭐

int __compute_return_epc_for_insn (struct pt_regs *regs , union
       mips_instruction insn );

two arguments, one int coming back at you. slay. 💅

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🎀 ARGUMENTS 🎀

• regs — pointer to pt_regs. that's the pointer. she points. periodt. 🫶
• insn — the branch instruction to decode. this is the one we're looking at, bestie. 🔍

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🔥 RETURN 🔥

• -EFAULT on error — and heads up, this one forces SIGILL. like, it does not play. 💀
• on success it returns 0 or BRANCH_LIKELY_TAKEN as appropriate, after evaluating the branch. iykyk. ✨

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🧚 DESCRIPTION 🧚

okay so this is the MIPS R6 Compact branches + forbidden slots situation, and honestly it's giving very specific lore, so let me break it down. 🌈

Compact branches do not throw exceptions because they do not have delay slots. iconic, no notes. 👑

The forbidden slot instruction ($PC+4) is only executed if the branch was not taken. Otherwise, the forbidden slot is skipped entirely — like, fully ghosted. 🙈

So what that means is: the only possible reason to be here because of a MIPS R6 compact branch instruction is that the forbidden slot has thrown one. 🫠 And in that case, the branch was not taken, so the EPC can be safely set to EPC + 8. boom. math. ate. 💖

no guessing, no improvising — that's literally the whole reasoning, bestie. 💜

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💜 SEE ALSO 💜

• Kernel file ./arch/mips/kernel/branch.c — go read her, she has the range. 📖

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and that's the page!! 🎉 this little icon lives in ./arch/mips/kernel, dated October 2026, and it's part of the Kernel API Manual. mwah. 💋✨💖