CPUID Instructions

CPUID instructions are complex instructions. It can be used to extract processor properties. CPUID instruction is a serializing instruction, i.e when executed, all concurrent, speculative and pipelined executions are stopped.

Information such as Processor, Cache/TLB, Cache Parameters, Performance Monitoring, L2 Cache information can be retrieved from user-space.


Refer to Intel Developer Instruction Manual.

typedef struct cpuid {
        uint32_t        eax;
        uint32_t        ebx;
        uint32_t        ecx;
        uint32_t        edx;
} cpuid_t;

static cpuid_t
get_cpu_id(uint32_t id)
{
        cpuid_t cpu;
        asm("mov %%ebx, %%esi\n\t"
                "cpuid\n\t"
                "xchg %%esi, %%ebx"
                : "=a"  (cpu.eax),
                  "=S"  (cpu.ebx),
                  "=c"  (cpu.ecx),
                  "=d"  (cpu.edx)
                : "a" (id)
        );
        return (cpu);
}

int
main()
{
        cpuid_t cpu;
        char    name[100];
        /* issue CPUID 0 instruction to read CPU information */
        cpu = get_cpu_id(0);
        printf("cpu.eax is %d\n", cpu.eax);
        sprintf(n, "%.4s%.4s%.4s\n", (char *)&cpu.ebx, (char *)&cpu.ecx, (char *)&cpu.edx);
        printf("processor name is %s\n", name);

        cpu = get_cpu_id(1);
        printf("Processor Type is %x\n", (cpu.eax & 0x00003000));
        printf("Family Type is %x\n", (cpu.eax & 0x00000F00) >> 8);

        cpu = get_cpu_id(0x80000008);
        printf("cache info phyMemory size %x\n", 1 << (cpu.eax & 0x0000000F));
        printf("cache info virtMemory %x\n", 1 << (cpu.eax >> 8));
}