check_seg_overrides(9)

✨ NAME ✨

okay so bestie, this is check_seg_overrides(9) from the Kernel API Manual — the function that literally checks if segment override prefixes are allowed. It's giving tiny-but-iconic kernel helper energy, and we're obsessed. 🎀

🛠️ SYNOPSIS 🛠️

No cap, the signature is exactly this:

bool check_seg_overrides (struct insn *insn , int regoff );

💅 ARGUMENTS 💅

• insn — a valid instruction with segment override prefixes. That's the instruction we're checking, and yes it has to be valid, bestie. ✨
• regoff — operand offset, in pt_regs, for which the check is performed. It's the exact offset in pt_regs where the vibe check happens. 🫶

🔍 DESCRIPTION 🔍

okay so here's the tea: for a particular register used in register-indirect addressing, this function determines if segment override prefixes can be used. Specifically, no overrides are allowed for rDI if used with a string instruction. That's the rule, periodt. 💀

It returns True if segment override prefixes can be used with the register indicated in regoff. False if otherwise. Literally that simple, iykyk. 🌈

👑 SEE ALSO 👑

These related besties live in the Kernel file ./arch/x86/lib/insn-eval.c:

• is_string_insn(9)
• insn_has_rep_prefix(9)
• get_seg_reg_override_idx(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)

💖 cute sign-off time: source/version is ./arch/x86/lib, date is October 2026, and the manual name is check_seg_overrides(9). stay slay, bestie 💅✨