/proc/cpuinfoでcpuの機能を表示するflagsのところってどうやって名称設定してんだろ？と思ったので調べてみたメモです。調べたカーネルのバージョンはv4.14.12です。

↓これですね f:id:masami256:20180110231210p:plain

/proc/cpuinfoのopen処理

これはfs/proc/cpuinfo.cにあるcpuinfo_open()が担当します。と言っても、実際の処理はseq_operations構造体のcpuinfo_opに関数がセットされていて、それらが実行されます。

extern const struct seq_operations cpuinfo_op;
static int cpuinfo_open(struct inode *inode, struct file *file)
{
    return seq_open(file, &cpuinfo_op);
}

ここからはアーキテクチャ固有になります。我らがx86_64ではarch/x86/kernel/cpu/proc.cにて以下のように設定を行っています。

onst struct seq_operations cpuinfo_op = {
    .start  = c_start,
    .next   = c_next,
    .stop   = c_stop,
    .show   = show_cpuinfo,
};

名前からしてshow_cpuinfo()を見れば良さそうに思えるのでこれを見てみます。

show_cpuinfo()

show_cpuinfo()が実際にcpuの情報を表示する関数です。

上から見ていくとこのようなところがみつかります。ここがflagsを出しているとこですね。

 seq_puts(m, "flags\t\t:");
    for (i = 0; i < 32*NCAPINTS; i++)
        if (cpu_has(c, i) && x86_cap_flags[i] != NULL)
            seq_printf(m, " %s", x86_cap_flags[i]);

seq_printf()はフォーマット指定子に%sを使っていて、引数はx86_cap_flags[i]なので、配列のx86_cap_flagsに名称が入ってるのがわかります。そしたらx86_cap_flagsがどこで設定されてるか調べればOKですね。

x86_cap_flags配列

この配列ですが使ってるファイルは3ファイルです。

f:id:masami256:20180110232436p:plain

で、実際にこの配列に値を設定している箇所はmakeの実行前には存在しません(´・ω・`)　なので、elixir.free-electrons.comだと見れないんですね。

x86_cap_flags配列の設定

ここで手元のカーネルになるので4.15.0-rc7になるんですが、arch/x86/kernel/cpu/capflags.cが設定している感じですね。

masami@saga:~/linux-kernel (test %)$ find arch/x86 -name "*.c" -o -name "*.h" | xargs grep -n "x86_cap_flags"
arch/x86/kernel/cpu/proc.c:102:         if (cpu_has(c, i) && x86_cap_flags[i] != NULL)
arch/x86/kernel/cpu/proc.c:103:                 seq_printf(m, " %s", x86_cap_flags[i]);
arch/x86/kernel/cpu/capflags.c:5:const char * const x86_cap_flags[NCAPINTS*32] = {
arch/x86/boot/mkcpustr.c:32:                    str = x86_cap_flags[i*32+j];
arch/x86/include/asm/cpufeature.h:35:extern const char * const x86_cap_flags[NCAPINTS*32];
arch/x86/include/asm/cpufeature.h:38:#define x86_cap_flag(flag) x86_cap_flags[flag]

このファイルはこんな内容です。

#ifndef _ASM_X86_CPUFEATURES_H
#include <asm/cpufeatures.h>
#endif

const char * const x86_cap_flags[NCAPINTS*32] = {
    [X86_FEATURE_FPU]        = "fpu",
    [X86_FEATURE_VME]        = "vme",
    [X86_FEATURE_DE]         = "de",
    [X86_FEATURE_PSE]        = "pse",
    [X86_FEATURE_TSC]        = "tsc",
    [X86_FEATURE_MSR]        = "msr",
    [X86_FEATURE_PAE]        = "pae",
    [X86_FEATURE_MCE]        = "mce",
    [X86_FEATURE_CX8]        = "cx8",
    [X86_FEATURE_APIC]       = "apic",
    [X86_FEATURE_SEP]        = "sep",
    [X86_FEATURE_MTRR]       = "mtrr",
    [X86_FEATURE_PGE]        = "pge",
    [X86_FEATURE_MCA]        = "mca",
    [X86_FEATURE_CMOV]       = "cmov",
    [X86_FEATURE_PAT]        = "pat",
    [X86_FEATURE_PSE36]      = "pse36",
    [X86_FEATURE_PN]         = "pn",
    [X86_FEATURE_CLFLUSH]        = "clflush",
    [X86_FEATURE_DS]         = "dts",
    [X86_FEATURE_ACPI]       = "acpi",
    [X86_FEATURE_MMX]        = "mmx",
    [X86_FEATURE_FXSR]       = "fxsr",
    [X86_FEATURE_XMM]        = "sse",
    [X86_FEATURE_XMM2]       = "sse2",
    [X86_FEATURE_SELFSNOOP]      = "ss",
    [X86_FEATURE_HT]         = "ht",
    [X86_FEATURE_ACC]        = "tm",
    [X86_FEATURE_IA64]       = "ia64",
    [X86_FEATURE_PBE]        = "pbe",
    [X86_FEATURE_SYSCALL]        = "syscall",
    [X86_FEATURE_MP]         = "mp",
    [X86_FEATURE_NX]         = "nx",
    [X86_FEATURE_MMXEXT]         = "mmxext",
    [X86_FEATURE_FXSR_OPT]       = "fxsr_opt",
    [X86_FEATURE_GBPAGES]        = "pdpe1gb",
    [X86_FEATURE_RDTSCP]         = "rdtscp",
    [X86_FEATURE_LM]         = "lm",
    [X86_FEATURE_3DNOWEXT]       = "3dnowext",
    [X86_FEATURE_3DNOW]      = "3dnow",
    [X86_FEATURE_RECOVERY]       = "recovery",
    [X86_FEATURE_LONGRUN]        = "longrun",
    [X86_FEATURE_LRTI]       = "lrti",
    [X86_FEATURE_CXMMX]      = "cxmmx",
    [X86_FEATURE_K6_MTRR]        = "k6_mtrr",
    [X86_FEATURE_CYRIX_ARR]      = "cyrix_arr",
    [X86_FEATURE_CENTAUR_MCR]    = "centaur_mcr",
    [X86_FEATURE_CONSTANT_TSC]   = "constant_tsc",
    [X86_FEATURE_UP]         = "up",
    [X86_FEATURE_ART]        = "art",
    [X86_FEATURE_ARCH_PERFMON]   = "arch_perfmon",
    [X86_FEATURE_PEBS]       = "pebs",
    [X86_FEATURE_BTS]        = "bts",
    [X86_FEATURE_REP_GOOD]       = "rep_good",
    [X86_FEATURE_ACC_POWER]      = "acc_power",
    [X86_FEATURE_NOPL]       = "nopl",
    [X86_FEATURE_XTOPOLOGY]      = "xtopology",
    [X86_FEATURE_TSC_RELIABLE]   = "tsc_reliable",
    [X86_FEATURE_NONSTOP_TSC]    = "nonstop_tsc",
    [X86_FEATURE_CPUID]      = "cpuid",
    [X86_FEATURE_EXTD_APICID]    = "extd_apicid",
    [X86_FEATURE_AMD_DCM]        = "amd_dcm",
    [X86_FEATURE_APERFMPERF]     = "aperfmperf",
    [X86_FEATURE_NONSTOP_TSC_S3]     = "nonstop_tsc_s3",
    [X86_FEATURE_TSC_KNOWN_FREQ]     = "tsc_known_freq",
    [X86_FEATURE_XMM3]       = "pni",
    [X86_FEATURE_PCLMULQDQ]      = "pclmulqdq",
    [X86_FEATURE_DTES64]         = "dtes64",
    [X86_FEATURE_MWAIT]      = "monitor",
    [X86_FEATURE_DSCPL]      = "ds_cpl",
    [X86_FEATURE_VMX]        = "vmx",
    [X86_FEATURE_SMX]        = "smx",
    [X86_FEATURE_EST]        = "est",
    [X86_FEATURE_TM2]        = "tm2",
    [X86_FEATURE_SSSE3]      = "ssse3",
    [X86_FEATURE_CID]        = "cid",
    [X86_FEATURE_SDBG]       = "sdbg",
    [X86_FEATURE_FMA]        = "fma",
    [X86_FEATURE_CX16]       = "cx16",
    [X86_FEATURE_XTPR]       = "xtpr",
    [X86_FEATURE_PDCM]       = "pdcm",
    [X86_FEATURE_PCID]       = "pcid",
    [X86_FEATURE_DCA]        = "dca",
    [X86_FEATURE_XMM4_1]         = "sse4_1",
    [X86_FEATURE_XMM4_2]         = "sse4_2",
    [X86_FEATURE_X2APIC]         = "x2apic",
    [X86_FEATURE_MOVBE]      = "movbe",
    [X86_FEATURE_POPCNT]         = "popcnt",
    [X86_FEATURE_TSC_DEADLINE_TIMER] = "tsc_deadline_timer",
    [X86_FEATURE_AES]        = "aes",
    [X86_FEATURE_XSAVE]      = "xsave",
    [X86_FEATURE_AVX]        = "avx",
    [X86_FEATURE_F16C]       = "f16c",
    [X86_FEATURE_RDRAND]         = "rdrand",
    [X86_FEATURE_HYPERVISOR]     = "hypervisor",
    [X86_FEATURE_XSTORE]         = "rng",
    [X86_FEATURE_XSTORE_EN]      = "rng_en",
    [X86_FEATURE_XCRYPT]         = "ace",
    [X86_FEATURE_XCRYPT_EN]      = "ace_en",
    [X86_FEATURE_ACE2]       = "ace2",
    [X86_FEATURE_ACE2_EN]        = "ace2_en",
    [X86_FEATURE_PHE]        = "phe",
    [X86_FEATURE_PHE_EN]         = "phe_en",
    [X86_FEATURE_PMM]        = "pmm",
    [X86_FEATURE_PMM_EN]         = "pmm_en",
    [X86_FEATURE_LAHF_LM]        = "lahf_lm",
    [X86_FEATURE_CMP_LEGACY]     = "cmp_legacy",
    [X86_FEATURE_SVM]        = "svm",
    [X86_FEATURE_EXTAPIC]        = "extapic",
    [X86_FEATURE_CR8_LEGACY]     = "cr8_legacy",
    [X86_FEATURE_ABM]        = "abm",
    [X86_FEATURE_SSE4A]      = "sse4a",
    [X86_FEATURE_MISALIGNSSE]    = "misalignsse",
    [X86_FEATURE_3DNOWPREFETCH]  = "3dnowprefetch",
    [X86_FEATURE_OSVW]       = "osvw",
    [X86_FEATURE_IBS]        = "ibs",
    [X86_FEATURE_XOP]        = "xop",
    [X86_FEATURE_SKINIT]         = "skinit",
    [X86_FEATURE_WDT]        = "wdt",
    [X86_FEATURE_LWP]        = "lwp",
    [X86_FEATURE_FMA4]       = "fma4",
    [X86_FEATURE_TCE]        = "tce",
    [X86_FEATURE_NODEID_MSR]     = "nodeid_msr",
    [X86_FEATURE_TBM]        = "tbm",
    [X86_FEATURE_TOPOEXT]        = "topoext",
    [X86_FEATURE_PERFCTR_CORE]   = "perfctr_core",
    [X86_FEATURE_PERFCTR_NB]     = "perfctr_nb",
    [X86_FEATURE_BPEXT]      = "bpext",
    [X86_FEATURE_PTSC]       = "ptsc",
    [X86_FEATURE_PERFCTR_LLC]    = "perfctr_llc",
    [X86_FEATURE_MWAITX]         = "mwaitx",
    [X86_FEATURE_RING3MWAIT]     = "ring3mwait",
    [X86_FEATURE_CPUID_FAULT]    = "cpuid_fault",
    [X86_FEATURE_CPB]        = "cpb",
    [X86_FEATURE_EPB]        = "epb",
    [X86_FEATURE_CAT_L3]         = "cat_l3",
    [X86_FEATURE_CAT_L2]         = "cat_l2",
    [X86_FEATURE_CDP_L3]         = "cdp_l3",
    [X86_FEATURE_INVPCID_SINGLE]     = "invpcid_single",
    [X86_FEATURE_HW_PSTATE]      = "hw_pstate",
    [X86_FEATURE_PROC_FEEDBACK]  = "proc_feedback",
    [X86_FEATURE_SME]        = "sme",
    [X86_FEATURE_PTI]        = "pti",
    [X86_FEATURE_INTEL_PPIN]     = "intel_ppin",
    [X86_FEATURE_INTEL_PT]       = "intel_pt",
    [X86_FEATURE_AVX512_4VNNIW]  = "avx512_4vnniw",
    [X86_FEATURE_AVX512_4FMAPS]  = "avx512_4fmaps",
    [X86_FEATURE_MBA]        = "mba",
    [X86_FEATURE_TPR_SHADOW]     = "tpr_shadow",
    [X86_FEATURE_VNMI]       = "vnmi",
    [X86_FEATURE_FLEXPRIORITY]   = "flexpriority",
    [X86_FEATURE_EPT]        = "ept",
    [X86_FEATURE_VPID]       = "vpid",
    [X86_FEATURE_VMMCALL]        = "vmmcall",
    [X86_FEATURE_FSGSBASE]       = "fsgsbase",
    [X86_FEATURE_TSC_ADJUST]     = "tsc_adjust",
    [X86_FEATURE_BMI1]       = "bmi1",
    [X86_FEATURE_HLE]        = "hle",
    [X86_FEATURE_AVX2]       = "avx2",
    [X86_FEATURE_SMEP]       = "smep",
    [X86_FEATURE_BMI2]       = "bmi2",
    [X86_FEATURE_ERMS]       = "erms",
    [X86_FEATURE_INVPCID]        = "invpcid",
    [X86_FEATURE_RTM]        = "rtm",
    [X86_FEATURE_CQM]        = "cqm",
    [X86_FEATURE_MPX]        = "mpx",
    [X86_FEATURE_RDT_A]      = "rdt_a",
    [X86_FEATURE_AVX512F]        = "avx512f",
    [X86_FEATURE_AVX512DQ]       = "avx512dq",
    [X86_FEATURE_RDSEED]         = "rdseed",
    [X86_FEATURE_ADX]        = "adx",
    [X86_FEATURE_SMAP]       = "smap",
    [X86_FEATURE_AVX512IFMA]     = "avx512ifma",
    [X86_FEATURE_CLFLUSHOPT]     = "clflushopt",
    [X86_FEATURE_CLWB]       = "clwb",
    [X86_FEATURE_AVX512PF]       = "avx512pf",
    [X86_FEATURE_AVX512ER]       = "avx512er",
    [X86_FEATURE_AVX512CD]       = "avx512cd",
    [X86_FEATURE_SHA_NI]         = "sha_ni",
    [X86_FEATURE_AVX512BW]       = "avx512bw",
    [X86_FEATURE_AVX512VL]       = "avx512vl",
    [X86_FEATURE_XSAVEOPT]       = "xsaveopt",
    [X86_FEATURE_XSAVEC]         = "xsavec",
    [X86_FEATURE_XGETBV1]        = "xgetbv1",
    [X86_FEATURE_XSAVES]         = "xsaves",
    [X86_FEATURE_CQM_LLC]        = "cqm_llc",
    [X86_FEATURE_CQM_OCCUP_LLC]  = "cqm_occup_llc",
    [X86_FEATURE_CQM_MBM_TOTAL]  = "cqm_mbm_total",
    [X86_FEATURE_CQM_MBM_LOCAL]  = "cqm_mbm_local",
    [X86_FEATURE_CLZERO]         = "clzero",
    [X86_FEATURE_IRPERF]         = "irperf",
    [X86_FEATURE_XSAVEERPTR]     = "xsaveerptr",
    [X86_FEATURE_DTHERM]         = "dtherm",
    [X86_FEATURE_IDA]        = "ida",
    [X86_FEATURE_ARAT]       = "arat",
    [X86_FEATURE_PLN]        = "pln",
    [X86_FEATURE_PTS]        = "pts",
    [X86_FEATURE_HWP]        = "hwp",
    [X86_FEATURE_HWP_NOTIFY]     = "hwp_notify",
    [X86_FEATURE_HWP_ACT_WINDOW]     = "hwp_act_window",
    [X86_FEATURE_HWP_EPP]        = "hwp_epp",
    [X86_FEATURE_HWP_PKG_REQ]    = "hwp_pkg_req",
    [X86_FEATURE_NPT]        = "npt",
    [X86_FEATURE_LBRV]       = "lbrv",
    [X86_FEATURE_SVML]       = "svm_lock",
    [X86_FEATURE_NRIPS]      = "nrip_save",
    [X86_FEATURE_TSCRATEMSR]     = "tsc_scale",
    [X86_FEATURE_VMCBCLEAN]      = "vmcb_clean",
    [X86_FEATURE_FLUSHBYASID]    = "flushbyasid",
    [X86_FEATURE_DECODEASSISTS]  = "decodeassists",
    [X86_FEATURE_PAUSEFILTER]    = "pausefilter",
    [X86_FEATURE_PFTHRESHOLD]    = "pfthreshold",
    [X86_FEATURE_AVIC]       = "avic",
    [X86_FEATURE_V_VMSAVE_VMLOAD]    = "v_vmsave_vmload",
    [X86_FEATURE_VGIF]       = "vgif",
    [X86_FEATURE_AVX512VBMI]     = "avx512vbmi",
    [X86_FEATURE_UMIP]       = "umip",
    [X86_FEATURE_PKU]        = "pku",
    [X86_FEATURE_OSPKE]      = "ospke",
    [X86_FEATURE_AVX512_VBMI2]   = "avx512_vbmi2",
    [X86_FEATURE_GFNI]       = "gfni",
    [X86_FEATURE_VAES]       = "vaes",
    [X86_FEATURE_VPCLMULQDQ]     = "vpclmulqdq",
    [X86_FEATURE_AVX512_VNNI]    = "avx512_vnni",
    [X86_FEATURE_AVX512_BITALG]  = "avx512_bitalg",
    [X86_FEATURE_AVX512_VPOPCNTDQ]   = "avx512_vpopcntdq",
    [X86_FEATURE_LA57]       = "la57",
    [X86_FEATURE_RDPID]      = "rdpid",
    [X86_FEATURE_OVERFLOW_RECOV]     = "overflow_recov",
    [X86_FEATURE_SUCCOR]         = "succor",
    [X86_FEATURE_SMCA]       = "smca",
};

const char * const x86_bug_flags[NBUGINTS*32] = {
    [X86_BUG_F00F - NCAPINTS*32]        = "f00f",
    [X86_BUG_FDIV - NCAPINTS*32]        = "fdiv",
    [X86_BUG_COMA - NCAPINTS*32]        = "coma",
    [X86_BUG_AMD_TLB_MMATCH - NCAPINTS*32]  = "tlb_mmatch",
    [X86_BUG_AMD_APIC_C1E - NCAPINTS*32]    = "apic_c1e",
    [X86_BUG_11AP - NCAPINTS*32]        = "11ap",
    [X86_BUG_FXSAVE_LEAK - NCAPINTS*32]     = "fxsave_leak",
    [X86_BUG_CLFLUSH_MONITOR - NCAPINTS*32]     = "clflush_monitor",
    [X86_BUG_SYSRET_SS_ATTRS - NCAPINTS*32]     = "sysret_ss_attrs",
    [X86_BUG_NULL_SEG - NCAPINTS*32]    = "null_seg",
    [X86_BUG_SWAPGS_FENCE - NCAPINTS*32]    = "swapgs_fence",
    [X86_BUG_MONITOR - NCAPINTS*32]         = "monitor",
    [X86_BUG_AMD_E400 - NCAPINTS*32]    = "amd_e400",
    [X86_BUG_CPU_MELTDOWN - NCAPINTS*32]    = "cpu_meltdown",
};

そして、このファイルがどのように作られるかと言うと、./arch/x86/kernel/cpu/Makefileの以下の部分です。mkcapflags.shというシェルスクリプトを実行してそこからファイルを作ってます。

ifdef CONFIG_X86_FEATURE_NAMES
quiet_cmd_mkcapflags = MKCAP   $@
      cmd_mkcapflags = $(CONFIG_SHELL) $(srctree)/$(src)/mkcapflags.sh $< $@

cpufeature = $(src)/../../include/asm/cpufeatures.h

targets += capflags.c
$(obj)/capflags.c: $(cpufeature) $(src)/mkcapflags.sh FORCE
    $(call if_changed,mkcapflags)
endif