vm86(2)

💖 vm86 — bestie edition (section 2 of the manual, the System Calls Manual, iykyk) 💖

✨ NAME ✨

vm86old, vm86 — enter virtual 8086 mode 🦋

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📚 LIBRARY 📚

Standard C library (libc, -lc) — she's already in your group chat, no install needed 💅

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🌸 SYNOPSIS 🌸

#include <sys/vm86.h>

int vm86old(struct vm86_struct *info);
int vm86(unsigned long fn, struct vm86plus_struct *v86);

okay so literally just two tiny calls and you're in another mode entirely, no cap ✨

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👑 DESCRIPTION 👑

The system call vm86() was introduced in Linux 0.97p2. Then in Linux 2.1.15 and 2.0.28, it got renamed to vm86old(), and a brand-new vm86() showed up to take its place 🫶. And the definition of struct vm86_struct got changed in 1.1.8 and 1.1.9 — so yeah, this whole thing has had a glow-up or two, fr fr.

These calls cause the process to enter VM86 mode (that's virtual-8086 if you're reading the Intel literature, bestie 📖), and they're used by dosemu 👑.

VM86 mode is an emulation of real mode within a protected mode task. It's giving "living your best retro life inside a modern apartment" and honestly? iconic. 💖

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🔥 RETURN VALUE 🔥

Slay: on success, zero is returned ✨. On error, -1 is returned, and errno is set to indicate the error. Classic. No notes. 😭

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💀 ERRORS 💀

• EFAULT — this return value is specific to i386 and indicates a problem with getting user-space data. She tried to grab your stuff and just… couldn't 🫠.
• ENOSYS — this return value indicates the call is not implemented on the present architecture. Wrong building, hon 💅.
• EPERM — saved kernel stack exists. (This is a kernel sanity check; the saved stack should exist only within vm86 mode itself.) So like, if you're seeing this and you're not in vm86 mode? That's a red flag, bestie 🚩.

⚠️ heads up: that EPERM one is the kernel doing a little vibe check on itself. The saved stack has no business existing outside vm86 mode, periodt.

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🌈 STANDARDS 🌈

Linux on 32-bit Intel processors. That's the whole vibe check, no cap 💜

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✨ that's the whole page, bestie — now go forth and virtualize ✨

This lil masterpiece is from Linux man-pages 6.20, dated 2026-02-08 🎀 mwah, drink water, and remember: man pages are just lore drops for your terminal 💖🦋🌸