Thursday, December 11, 2014

Checking whether hardware supports crypto instructions

A quick example of how to tell if the machine that you're running on supports crypto instructions.

The 2011 SPARC Architecture manual tells you to read the cfr register before using the instruction. The cfr register contains a bit for every implemented crypto instruction. However, the cfr register is not implemented on all processors. So you would need to check whether this register is implemented before reading it....

So there has to be a better way. Fortunately, Solaris implements a getisax() call which provides this information without the user needing to muck around with the low level details. The following code shows how this call can be used to check whether the AES instruction is implemented or not:

#include <sys/auxv.h>
#include <stdio.h>

void main()
  unsigned int array[10];
  unsigned int count = getisax(array,10);
  if (count>0)
    printf(" AES: ");
    if (array[0] & AV_SPARC_AES) { printf("Yes\n"); } else { printf("No\n"); }
    printf("Error: getisax() call returned no results\n");