insn_get_code_seg_params(9)

💅 insn_get_code_seg_params 💅

okay so this is a page from the Kernel API Manual, and we're about to make code-segment parameters make sense, bestie, no cap 🫶

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🌸 NAME 🌸

insn_get_code_seg_params — Obtain code segment parameters ✨

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🎀 SYNOPSIS 🎀

int insn_get_code_seg_params (struct pt_regs *regs );

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🦋 ARGUMENTS 🦋

• regs — Structure with register values as seen when entering kernel mode. it's giving "snapshot of the moment we hopped into the kernel" energy 💫

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💖 DESCRIPTION 💖

so the whole point of this one is: Obtain address and operand sizes of the code segment. literally that's the job 👑

and where does it get them from?? from the selector contained in the CS register in regs. iykyk 🧚

now, in protected mode, the default address is determined by inspecting the L and D bits of the segment descriptor. yes bestie, you gotta actually go look at the descriptor bits, we don't just guess 💅

in virtual-8086 mode tho? the default is always two bytes for both address and operand sizes. always. every time. periodt. 🎯

so what comes back to you:

• An int containing ORed-in default parameters on success. slay 🥳
• -EINVAL on error. 😭 it happens to the best of us.

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🌈 SEE ALSO 🌈

the whole friend group lives in ./arch/x86/lib/insn-eval.c, and here's the full roster — every single one of them, no skips 🙈:

• 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_segment_selector(9)
• get_reg_offset_16(9)
• get_desc(9)
• insn_get_seg_base(9)
• get_seg_limit(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)

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and that's the page!! brought to you by the fine folks over in ./arch/x86/lib, dated October 2026 — mwah, love u, go read some segment descriptors 💜✨🎀