rapid7/metasploit-framework

/*
 * outputs a cpuid key for use in context keyed payload encoding.
 *
 * Author: Dimitris Glynos <dimitris at census-labs.com>
 */


#include <stdio.h>

int main()
{
    unsigned long eax;

        asm (
        "xorl %%esi, %%esi;" /* esi is key store, zero it out */
        "xorl %%edi, %%edi;" /* edi is loop iterator, ditto */
        "cpuid_loop: movl %%edi, %%eax;" /* iterator is first arg 
                                                    to cpuid */
        "xorl %%ecx, %%ecx;" /* ecx is also used as arg to cpuid but
                                        we'll use it always as zero */
        "cpuid;"
        "xorl %%eax, %%esi;"
        "cmpl %%esi, %%eax;"     /* first time round esi = eax */
                    /* not very safe heh? */
        "jne not_first_time;"
        "leal 0x1(%%eax, 1), %%edi;" /* first time round ... */
        "not_first_time: xorl %%ebx, %%esi;"
        "xorl %%ecx, %%esi;"
        "xorl %%edx, %%esi;"
        "subl $1, %%edi;"
        "jne cpuid_loop;"
        "movl %%esi, %%eax;"
                : "=a" (eax)
        );

    printf("%#.8lx\n", eax);
    return 0;
}