xsaves(9)

💅 xsaves(9) — Kernel API Manual energy ✨

okay so bestie, welcome to the Kernel API Manual 💖 this one is all about xsaves, and she is literally the “save selected components to a kernel xstate buffer” girlie. no cap. let’s get into it 🫶

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✨ NAME ✨

• xsaves — save selected components to a kernel xstate buffer 🌸

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🎀 SYNOPSIS 🎀

the whole signature is giving short, sweet, and very “copy me exactly”:

void xsaves (struct xregs_state *xstate , u64 mask );

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💖 ARGUMENTS 💖

• xstate — pointer to the buffer 🦋
• mask — feature mask to select the components to save ✨

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🔥 DESCRIPTION 🔥

okay so the xstate buffer has two non-negotiables, and I need you to take notes 📝: it must be 64 byte aligned, and it must be correctly initialized. why? because XSAVES does not write the full xstate header — and the way that omission can ruin your whole entire day is real 😭.

Before first use, the buffer should be zeroed. seriously. if you don’t, a consecutive XRSTORS from that buffer can #GP, and that is the kind of plot twist nobody asked for 💀.

also, the feature mask must be a subset of the independent features. that’s the vibe check for mask, bestie ✅.

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🌈 SEE ALSO 🌈

• Kernel file ./arch/x86/kernel/fpu/xstate.c — the source, bestie, go read it 📖
• check_xtile_data_against_struct(9) 🧚
• __copy_xstate_to_uabi_buf(9) 💜
• copy_xstate_to_uabi_buf(9) 🫶
• copy_uabi_to_xstate(9) ⭐
• xrstors(9) 👑
• fpstate_realloc(9) 🍓
• fpu_xstate_prctl(9) 💅

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mwah 💋 this page is repping the ./arch/x86/kernel/fpu source/version and the October 2026 date — that’s the footer energy, and honestly? iconic. periodt. 🎀✨