Linux 上的 /proc是一个虚拟文件系统，在系统启动后挂载在 /proc 上，/proc 包含了很多内核和系统信息用来展示 Linux 内核是如何展示硬件的，比如在 /proc/cpuinfo 里可以看到一些关于 CPU 的信息，其中的 flags 包含了很多用来表示 CPU 特征的参数：
$ cat /proc/cpuinfo | grep flags flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts rep_good xtopology nonstop_tsc aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm sse4_1 sse4_2 popcnt lahf_lm arat tpr_shadow vnmi flexpriority ept vpid
具体每个 flag 缩写代表什么意思呢？关于 Linux 的最权威答案永远来自源代码，VPSee 在内核源代码里找到了每个 flag 的相关注释，通过这些注释可以很方便我们理解这些 flags 缩写：
# vi /home/vpsee/linux-2.6.31.8/arch/x86/include/asm/cpufeature.h
...
/* Intel-defined CPU features, CPUID level 0x00000001 (edx), word 0 */
#define X86_FEATURE_FPU (0*32+ 0) /* Onboard FPU */
#define X86_FEATURE_VME (0*32+ 1) /* Virtual Mode Extensions */
#define X86_FEATURE_DE (0*32+ 2) /* Debugging Extensions */
#define X86_FEATURE_PSE (0*32+ 3) /* Page Size Extensions */
#define X86_FEATURE_TSC (0*32+ 4) /* Time Stamp Counter */
#define X86_FEATURE_MSR (0*32+ 5) /* Model-Specific Registers */
#define X86_FEATURE_PAE (0*32+ 6) /* Physical Address Extensions */
#define X86_FEATURE_MCE (0*32+ 7) /* Machine Check Exception */
#define X86_FEATURE_CX8 (0*32+ 8) /* CMPXCHG8 instruction */
#define X86_FEATURE_APIC (0*32+ 9) /* Onboard APIC */
#define X86_FEATURE_SEP (0*32+11) /* SYSENTER/SYSEXIT */
#define X86_FEATURE_MTRR (0*32+12) /* Memory Type Range Registers */
#define X86_FEATURE_PGE (0*32+13) /* Page Global Enable */
#define X86_FEATURE_MCA (0*32+14) /* Machine Check Architecture */
#define X86_FEATURE_CMOV (0*32+15) /* CMOV instructions */
/* (plus FCMOVcc, FCOMI with FPU) */
#define X86_FEATURE_PAT (0*32+16) /* Page Attribute Table */
#define X86_FEATURE_PSE36 (0*32+17) /* 36-bit PSEs */
#define X86_FEATURE_PN (0*32+18) /* Processor serial number */
#define X86_FEATURE_CLFLSH (0*32+19) /* "clflush" CLFLUSH instruction */
#define X86_FEATURE_DS (0*32+21) /* "dts" Debug Store */
#define X86_FEATURE_ACPI (0*32+22) /* ACPI via MSR */
#define X86_FEATURE_MMX (0*32+23) /* Multimedia Extensions */
#define X86_FEATURE_FXSR (0*32+24) /* FXSAVE/FXRSTOR, CR4.OSFXSR */
#define X86_FEATURE_XMM (0*32+25) /* "sse" */
#define X86_FEATURE_XMM2 (0*32+26) /* "sse2" */
#define X86_FEATURE_SELFSNOOP (0*32+27) /* "ss" CPU self snoop */
#define X86_FEATURE_HT (0*32+28) /* Hyper-Threading */
#define X86_FEATURE_ACC (0*32+29) /* "tm" Automatic clock control */
#define X86_FEATURE_IA64 (0*32+30) /* IA-64 processor */
#define X86_FEATURE_PBE (0*32+31) /* Pending Break Enable */
/* AMD-defined CPU features, CPUID level 0x80000001, word 1 */
/* Don't duplicate feature flags which are redundant with Intel! */
#define X86_FEATURE_SYSCALL (1*32+11) /* SYSCALL/SYSRET */
#define X86_FEATURE_MP (1*32+19) /* MP Capable. */
#define X86_FEATURE_NX (1*32+20) /* Execute Disable */
#define X86_FEATURE_MMXEXT (1*32+22) /* AMD MMX extensions */
#define X86_FEATURE_FXSR_OPT (1*32+25) /* FXSAVE/FXRSTOR optimizations */
#define X86_FEATURE_GBPAGES (1*32+26) /* "pdpe1gb" GB pages */
#define X86_FEATURE_RDTSCP (1*32+27) /* RDTSCP */
#define X86_FEATURE_LM (1*32+29) /* Long Mode (x86-64) */
#define X86_FEATURE_3DNOWEXT (1*32+30) /* AMD 3DNow! extensions */
#define X86_FEATURE_3DNOW (1*32+31) /* 3DNow! */
...
/* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
...
/* VIA/Cyrix/Centaur-defined CPU features, CPUID level 0xC0000001, word 5 */
...
/* More extended AMD flags: CPUID level 0x80000001, ecx, word 6 */
...
仅有 flags 缩写和注释不足以理解 flag 的含义，但是足够发挥个人的 googleability 了，比如直接搜索 msr 不会得到任何有用信息，但是利用上面的注释搜索 Model-Specific Registers（google “Model-Specific Registers”）就会得到很多信息，学习的过程就是不断提高 googleability 的过程：）