insn_get_modrm_rm_off(9)

💅 insn_get_modrm_rm_off(9) 💅

okay bestie, welcome to the Kernel API Manual page for insn_get_modrm_rm_off — yes, the name is a whole mouthful, but we’re gonna slay it together. 🫶

✨ NAME ✨

insn_get_modrm_rm_off — obtain register in r/m part of the ModRM byte.

💖 SYNOPSIS 💖

int insn_get_modrm_rm_off (struct insn *insn , struct pt_regs *regs );

🎀 ARGUMENTS 🎀

• insn — instruction containing the ModRM byte. It’s the main character we’re inspecting. 💅
• regs — register values as seen when entering kernel mode. Basically the receipts from kernel entry. ✨

🦋 DESCRIPTION 🦋

The register indicated by the r/m part of the ModRM byte. The register is obtained as an offset from the base of pt_regs. In specific cases, the returned value can be -EDOM to indicate that the particular value of ModRM does not refer to a register and shall be ignored.

lowkey important: when that -EDOM shows up, it means “this ModRM value does not refer to a register, ignore it, bestie.” 😭

🌈 SEE ALSO 🌈

the whole linked-page squad, no skips: 💖

• Kernel file ./arch/x86/lib/insn-eval.c — 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_code_seg_params(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)

mwah 💋 — source/version ./arch/x86/lib, dated October 2026, for insn_get_modrm_rm_off(9). bestie, you’re gonna do amazing. 🫶✨