/*
 * Securely wipe memory.
 *
 * The actual wiping is no different from what memset would do: the
 * point of 'securely' is to try to be sure over-clever compilers
 * won't optimise away memsets on variables that are about to be freed
 * or go out of scope. See
 * https://buildsecurityin.us-cert.gov/bsi-rules/home/g1/771-BSI.html
 *
 * Some platforms (e.g. Windows) may provide their own version of this
 * function.
 */

#include "defs.h"
#include "misc.h"

void smemclr(void *b, size_t n)
{
    volatile char *vp;

    if (b && n > 0) {
        /*
         * Zero out the memory.
         */
        memset(b, 0, n);

        /*
         * Perform a volatile access to the object, forcing the
         * compiler to admit that the previous memset was important.
         *
         * This while loop should in practice run for zero iterations
         * (since we know we just zeroed the object out), but in
         * theory (as far as the compiler knows) it might range over
         * the whole object. (If we had just written, say, '*vp =
         * *vp;', a compiler could in principle have 'helpfully'
         * optimised the memset into only zeroing out the first byte.
         * This should be robust.)
         */
        vp = b;
        while (*vp) vp++;
    }
}