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cpuid.c

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdbool.h>
 
void print_chars(uint64_t num);
bool isvischar(char ch);
 
int main(int argc, const char * argv[]) {
  if (argc != 2) {
    fprintf(stderr, "Usage: %s <RAX value>\n", argv[0]);
    return 0;
  }
 
  uint64_t rbx, rdx, rcx;
  __asm__("xor %%rdx, %%rdx\n"
          "xor %%rcx, %%rcx\n"
          "xor %%rbx, %%rbx\n"
          "cpuid"
          : "=b" (rbx), "=d" (rdx), "=c" (rcx)
          : "a" (atoll(argv[1])));
  printf("rbx=%08llx rdx=%08llx rcx=%08llx\n", rbx, rdx, rcx);
 
  printf("rbx=");
  print_chars(rbx);
  printf("     rdx=");
  print_chars(rdx);
  printf("     rcx=");
  print_chars(rcx);
  printf("\n");
 
  return 0;
}
 
void print_chars(uint64_t num) {
  uint64_t i;
  for (i = 0; i < 4; i++) {
    char ch = (char)(num & 0xff);
    if (isvischar(ch)) {
      printf("%c", ch);
    } else {
      printf(".");
    }
    num >>= 8;
  }
}
 
bool isvischar(char ch) {
  if (ch >= 0x20 && ch < 0x7f) return true;
  return false;
}