arch_enter_from_user_mode(9)

💅 arch_enter_from_user_mode(9) — Kernel API Manual, bestie edition

okay so real talk, this one's from the Kernel API Manual and it's literally the vibe check your CPU does when you come back from user mode. no cap, it's short, but it matters. 🦋

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✨ NAME ✨

arch_enter_from_user_mode — the architecture-specific sanity check for user mode regs 🎀

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✨ SYNOPSIS ✨

void arch_enter_from_user_mode (struct pt_regs *regs );

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✨ ARGUMENTS ✨

• regs — pointer to the current task's pt_regs. like, the receipts of where the CPU was. 🧾💖

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✨ DESCRIPTION ✨

so by default this is an empty implementation, like a blank notes app page waiting for you to write something. it can totally be replaced by architecture-specific code tho — every arch gets to do its own lil thing. 👑

it gets invoked from enter_from_user_mode in the non-instrumentable section. that's the whole point, bestie: it uses __always_inline so the compiler cannot push it out of line and make it instrumentable. absolutely not, not on our watch. 🚫🔍

lowkey iconic how a one-line function is doing this much structural work ngl 💀

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✨ SEE ALSO ✨

kernel file ./include/linux/irq-entry-common.h, plus the whole friend group:

• arch_in_rcu_eqs(9)
• enter_from_user_mode(9)
• arch_exit_to_user_mode_work(9)
• arch_exit_to_user_mode_prepare(9)
• arch_exit_to_user_mode(9)
• arch_do_signal_or_restart(9)
• __exit_to_user_mode_prepare(9)
• syscall_exit_to_user_mode_prepare(9)
• irqentry_exit_to_user_mode_prepare(9)
• exit_to_user_mode(9)
• irqentry_enter_from_user_mode(9)
• irqentry_exit_to_user_mode(9)
• struct irqentry_state(9)
• irqentry_enter_from_kernel_mode(9)
• irqentry_exit_to_kernel_mode_preempt(9)
• irqentry_exit_to_kernel_mode_after_preempt(9)
• irqentry_exit_to_kernel_mode(9)
• irqentry_enter(9)
• irqentry_exit(9)
• irqentry_nmi_enter(9)
• irqentry_nmi_exit(9)

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and that's the whole page, bestie!! 🌈 this lil icon lives in ./include/linux, it's dated October 2026, and it's serving arch_enter_from_user_mode(9) realness. go read the other ones too, iykyk 🫶💅✨