get_segment_selector(9)

💅 get_segment_selector(9) 💅

okay so this is from the Kernel API Manual, bestie, and it’s giving “we need a segment selector” energy ✨

🌸 NAME 🌸

• get_segment_selector — obtain segment selector 💖

✨ SYNOPSIS ✨

short get_segment_selector (struct pt_regs *regs , int seg_reg_idx );

🎀 ARGUMENTS 🎀

• regs — register values as seen when entering kernel mode 🫶
• seg_reg_idx — segment register index to use 👀

💖 DESCRIPTION 💖

okay so the whole point is to obtain the segment selector from any of the CS, SS, DS, ES, FS, GS segment registers. literally any of those six, she’s got you 💅

In CONFIG_X86_32, the segment is obtained from either pt_regs or kernel_vm86_regs as applicable. In CONFIG_X86_64, CS and SS are obtained from pt_regs. DS, ES, FS and GS are obtained by reading the actual CPU registers. This is done only for completeness, because in CONFIG_X86_64 segment registers are ignored 👑

what you get back:

• the value of the segment selector, including null when running in long mode 🌈
• -EINVAL on error 💀

🦋 SEE ALSO 🦋

these all live in the kernel file ./arch/x86/lib/insn-eval.c — go be nosy, bestie 👀

• is_string_insn(9)
• insn_has_rep_prefix(9)
• get_seg_reg_override_idx(9)
• check_seg_overrides(9)
• resolve_default_seg(9)
• resolve_seg_reg(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)

later bestie 💖 — source/version says ./arch/x86/lib, date says October 2026, and this whole page is get_segment_selector(9) 🦋✨