get_seg_reg_override_idx(9)

💅 get_seg_reg_override_idx 💅

okay so bestie, welcome to the Kernel API Manual entry for get_seg_reg_override_idx(9) — yes the man page name literally repeats the function name, that's just how these things roll, periodt. this one's lowkey a little detective mission through instruction prefixes and honestly it ate 💖

---

✨ NAME ✨

get_seg_reg_override_idx — obtain segment register override index 🎀

like, it gets you the index. for the segment register. for the override. you get it, i get it, we all get it 🫶

---

🌸 SYNOPSIS 🌸

int get_seg_reg_override_idx (struct insn *insn );

that's the whole vibe. one function, one argument, int coming back at you ✨

---

🦋 ARGUMENTS 🦋

• insn — a Valid instruction that's got segment override prefixes on it. bestie, note the capital-V Valid — this isn't a "sure, whatever, throw garbage in" situation, it needs to be a valid instruction with segment override prefixes and that's the whole assignment 💅

---

🧚 DESCRIPTION 🧚

so what it does is: it inspects the instruction prefixes inside insn and finds the segment overrides, if there are any. like a little scavenger hunt but for prefixes. main character energy fr fr 👑

what you get back is a constant identifying the segment register to use, and the roster is exactly: CS, SS, DS, ES, FS, or GS. one of those six, no substitutes, no additions 😌

now — if there were genuinely no segment override prefixes found? you get INAT_SEG_REG_DEFAULT back. that's the default, that's the fallback, that's the "nothing to see here, move along" answer 🌈

and if something goes wrong? -EINVAL in case of error. so yeah, error city, population: your return value 💀

ngl the whole thing is small but iconic. don't sleep on it.

---

💜 SEE ALSO 💜

okay so this section is a whole friend group and we're not leaving a single one of them out, so buckle up buttercup 🍓 — the kernel file is ./arch/x86/lib/insn-eval.c and here's the entire squad:

• is_string_insn(9)
• insn_has_rep_prefix(9)
• check_seg_overrides(9)
• resolve_default_seg(9)
• resolve_seg_reg(9)
• get_segment_selector(9)
• get_reg_offset_16(9)
• get_desc(9)
• insn_get_seg_base(9)
• get_seg_limit(9)
• insn_get_code_seg_params(9)
• insn_get_modrm_rm_off(9)
• insn_get_modrm_reg_off(9)
• insn_get_modrm_reg_ptr(9)
• get_seg_base_limit(9)
• get_eff_addr_reg(9)
• get_eff_addr_modrm(9)
• get_eff_addr_modrm_16(9)
• get_eff_addr_sib(9)
• get_addr_ref_16(9)
• get_addr_ref_32(9)
• get_addr_ref_64(9)
• insn_get_addr_ref(9)
• insn_fetch_from_user(9)
• insn_fetch_from_user_inatomic(9)
• insn_decode_from_regs(9)
• insn_decode_mmio(9)

every single one of them, accounted for, no bestie left behind 🫶✨

---

okay that's the page!! and for the cute sign-off: this lil masterpiece lives under ./arch/x86/lib, dated October 2026, and it's get_seg_reg_override_idx(9) all the way down. slay, go read your prefixes, mwah 💋💖