cpuid_subleaf_n(9)

✨ NAME ✨

okay so bestie, welcome to cpuid_subleaf_n(9) from the Kernel API Manual — this one is literally about how to access parsed CPUID data for a leaf that has a subleaf range. iconic behavior only 💅

cpuid_subleaf_n — access parsed CPUID data for leaf with a subleaf range. periodt.

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🌸 SYNOPSIS 🌸

cpuid_subleaf_n (_cpuinfo , _leaf , _subleaf );

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🎀 ARGUMENTS 🎀

• _cpuinfo — your CPU capability structure reference, aka a 'struct cpuinfo_x86'. yes bestie, that one 🫶
• _leaf — the CPUID leaf, in compile-time 0xN format; e.g. 0x4, 0x8000001d. no cap, the format matters ✨
• _subleaf — the subleaf number, and it can be passed dynamically. it must be smaller than cpuid_subleaf_count(_cpuinfo, _leaf). that's the vibe check it has to pass 💀

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🦋 DESCRIPTION 🦋

okay so here's the tea: build-time errors get emitted in these cases:

• _leaf has no subleaf range. leaves with a subleaf range have an _n type suffix and are listed at <asm/cpuid/types.h> using the CPUID_LEAF_N macro. so if your leaf isn't giving _n energy, that's a problem 🚩
• _subleaf is known at compile-time but is out of range. not me getting caught lacking at compile-time 🙈

Example usage, and yes it's giving main character energy:

            const struct leaf_0x4_n *l4;

            for (int i = 0; i < cpuid_subleaf_count(c, 0x4); i++) {
                    l4 = cpuid_subleaf_n(c, 0x4, i);
                    if (!l4) {
                            // Handle error
                    }
                    ...
            }

beside the standard error situations detailed at cpuid_subleaf, this macro will also return NULL if _subleaf is out of the leaf's subleaf range. so like… check your range, bestie 😭

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🌈 SEE ALSO 🌈

• Kernel file ./arch/x86/include/asm/cpuid/api.h
• cpuid_leaf_0x2(9)
• for_each_cpuid_0x2_desc(9)
• cpuid_subleaf(9)
• cpuid_leaf(9)
• cpuid_leaf_raw(9)
• cpuid_subleaf_n_raw(9)
• cpuid_subleaf_count(9)

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mwah 💋 that's the whole page — source/version: ./arch/x86/include/asm/cpuid, dated October 2026, and the manual page is cpuid_subleaf_n(9). slay 💖