reerre.cpp

static inline void native_cpuid(unsigned int *eax, unsigned int *ebx,
                                unsigned int *ecx, unsigned int *edx)
{
        /* ecx is often an input as well as an output. */
        asm volatile("cpuid"
            : "=a" (*eax),
              "=b" (*ebx),
              "=c" (*ecx),
              "=d" (*edx)
            : "0" (*eax), "2" (*ecx));
}
#include <stdio.h>

int main(int argc, char **argv)
{
  unsigned eax, ebx = 0, ecx = 0, edx = 0;
  eax = 0x40000000; /* processor serial number */
  native_cpuid(&eax, &ebx, &ecx, &edx);

        char buf[13] = {0};
        *(unsigned *)(&buf[0]) = ebx;
        *(unsigned *)(&buf[4]) = ecx;
        *(unsigned *)(&buf[8]) = edx;

  printf("serial number %s\n", buf);

}