none/tests/amd64/rdseed.c

   1
   2 #include <stdio.h>
   3 #include <stdlib.h>
   4 #include <assert.h>
   5 #include "tests/malloc.h"
   6
   7 typedef  unsigned char           UChar;
   8 typedef  unsigned int            UInt;
   9 typedef  unsigned long int       UWord;
  10 typedef  unsigned long long int  ULong;
  11
  12 // What can we actually test here?  The instructions take no input and
  13 // produce output which is by definition totally random.  So apart from
  14 // not simply failing insn decode, there's nothing much to test.
  15
  16 // Get 10 values of each size, and check that they are not all the same
  17 // (otherwise something's obviously wrong).  Now, statistically, it's
  18 // highly unlikely that they are all the same.  For 10 16 bit ints, the
  19 // probability of them being all the same is (I'd guess) (2^-16) ^ (10-1),
  20 // that is, 2^-144.
  21
  22 ULong do_rdseed64 ( void )
  23 {
  24    while (1) {
  25       ULong res = 0;
  26       ULong cflag = 0;
  27       __asm__ __volatile__(
  28          "movabsq $0x5555555555555555, %%r11 ; "
  29          "movq $0, %%r12 ; "
  30          "rdseed %%r11 ; "
  31          "setc %%r12b ; "
  32          "movq %%r11, %0 ; "
  33          "movq %%r12, %1"
  34          : "=r"(res), "=r"(cflag) : : "r11", "r12"
  35       );
  36       if (cflag == 1)
  37          return res;
  38    }
  39    /*NOTREACHED*/
  40 }
  41
  42 ULong do_rdseed32 ( void )
  43 {
  44    while (1) {
  45       ULong res = 0;
  46       ULong cflag = 0;
  47       __asm__ __volatile__(
  48          "movabsq $0x5555555555555555, %%r11 ; "
  49          "movq $0, %%r12 ; "
  50          "rdseed %%r11d ; "
  51          "setc %%r12b ; "
  52          "movq %%r11, %0 ; "
  53          "movq %%r12, %1"
  54          : "=r"(res), "=r"(cflag) : : "r11", "r12"
  55       );
  56       if (cflag == 1)
  57          return res;
  58    }
  59    /*NOTREACHED*/
  60 }
  61
  62 ULong do_rdseed16 ( void )
  63 {
  64    while (1) {
  65       ULong res = 0;
  66       ULong cflag = 0;
  67       __asm__ __volatile__(
  68          "movabsq $0x5555555555555555, %%r11 ; "
  69          "movq $0, %%r12 ; "
  70          "rdseed %%r11w ; "
  71          "setc %%r12b ; "
  72          "movq %%r11, %0 ; "
  73          "movq %%r12, %1"
  74          : "=r"(res), "=r"(cflag) : : "r11", "r12"
  75       );
  76       if (cflag == 1)
  77          return res;
  78    }
  79    /*NOTREACHED*/
  80 }
  81
  82 void do_test ( ULong(*fn)(void),
  83                ULong mask
  84                /* with 1s indicating the random bits in the result */ )
  85 {
  86    ULong arr[10];
  87    for (UInt i = 0; i < 10; i++) {
  88       arr[i] = fn();
  89    }
  90
  91    // They really should all be different (to an extremely high probabilty.
  92    // See comment above.
  93    int allSame = 1/*true*/; // really, a Bool
  94    for (UInt i = 1; i < 10; i++) {
  95       if (arr[i] != arr[0]) {
  96          allSame = 0/*false*/;
  97          break;
  98       }
  99    }
 100    assert(!allSame);
 101
 102    // The 0/32/48 leading bits of the result should have a particular value,
 103    // depending on the insn.  So print them, with the random part masked out.
 104    for (UInt i = 0; i < 10; i++) {
 105       printf("0x%016llx\n", arr[i] & ~mask);
 106    }
 107    printf("\n");
 108 }
 109
 110 int main ( void )
 111 {
 112    do_test( do_rdseed64, 0xFFFFFFFFFFFFFFFFULL );
 113    do_test( do_rdseed32, 0x00000000FFFFFFFFULL );
 114    do_test( do_rdseed16, 0x000000000000FFFFULL );
 115    return 0;
 116 }