[PATCH 2/3] Use urandom to get random seed

[Richard Guenther]

On Wed, Sep 28, 2011 at 2:49 PM, Andi Kleen <andi@firstfloor.org> wrote:
> From: Andi Kleen <ak@linux.intel.com>
>
> When available use /dev/urandom to get the random seem. This will lower the probability
> of collisions.
>
> On other systems it will fallback to the old methods.
>
> Passes bootstrap + testsuite on x86_64. Ok?
>
> gcc/:
>
> * 2011-09-26   Andi Kleen <ak@linux.intel.com>
>
>        * toplev.c (init_local_tick): Try reading random seed from /dev/urandom
> ---
>  gcc/toplev.c |   12 +++++++++++-
>  1 files changed, 11 insertions(+), 1 deletions(-)
>
> diff --git a/gcc/toplev.c b/gcc/toplev.c
> index 78583fc..ab6b5a4 100644
> --- a/gcc/toplev.c
> +++ b/gcc/toplev.c
> @@ -262,7 +262,17 @@ init_local_tick (void)
>  {
>   if (!flag_random_seed)
>     {
> -      /* Get some more or less random data.  */
> +      /* Try urandom first. Time of day is too likely to collide.
> +        In case of any error we just use the local tick. */
> +
> +      int fd = open ("/dev/urandom", O_RDONLY);
> +      if (fd >= 0)
> +        {
> +          read (fd, &random_seed, sizeof (random_seed));

I suppose we might get interrupted before anything is read and
read can return with -1 (I suppose partial reads are quite unlikely
though)?  Thus, don't we need the usual EINTR loop?

If not, the patch is ok.

Thanks,
Richard.

> +          close (fd);
> +        }
> +
> +      /* Now get the tick anyways  */
>  #ifdef HAVE_GETTIMEOFDAY
>       {
>        struct timeval tv;
> --
> 1.7.5.4
>
>