On Wed, Sep 20, 2017 at 10:39 PM, Alexander Monakov <[email protected]> wrote:
> Hi,
>
> Most compiler invocations don't actually need an entropy source, so
> open-read-close syscall sequence on /dev/urandom that GCC performs on
> each startup is useless (and can easily be avoided).
>
> This patch makes GCC read entropy from /dev/urandom lazily on first
> call to get_random_seed, and en passant cleans up some of the cruft.
>
> Tested on x86-64, OK to apply?
Ok.
Thanks,
Richard.
> Thanks.
> Alexander
>
> * toplev.h (set_random_seed): Adjust return type.
> * toplev.c (init_local_tick): Move eager initialization of random_seed
> to get_random_seed. Adjust comment.
> (init_random_seed): Inline to get_random_seed, delete.
> (get_random_seed): Initialize random_seed lazily.
> (set_random_seed): Do not return previous value.
> (print_switch_value): Do not call get_random_seed.
>
> diff --git a/gcc/toplev.c b/gcc/toplev.c
> index 7d2b8fffa0b..da2d7c566b1 100644
> --- a/gcc/toplev.c
> +++ b/gcc/toplev.c
> @@ -239,7 +239,7 @@ announce_function (tree decl)
> }
> }
>
> -/* Initialize local_tick with a random number or -1 if
> +/* Initialize local_tick with the time of day, or -1 if
> flag_random_seed is set. */
>
> static void
> @@ -247,19 +247,6 @@ init_local_tick (void)
> {
> if (!flag_random_seed)
> {
> - /* 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)
> - {
> - if (read (fd, &random_seed, sizeof (random_seed))
> - != sizeof (random_seed))
> - random_seed = 0;
> - close (fd);
> - }
> -
> - /* Now get the tick anyways */
> #ifdef HAVE_GETTIMEOFDAY
> {
> struct timeval tv;
> @@ -280,34 +267,33 @@ init_local_tick (void)
> local_tick = -1;
> }
>
> -/* Set up a default flag_random_seed and local_tick, unless the user
> - already specified one. Must be called after init_local_tick. */
> -
> -static void
> -init_random_seed (void)
> -{
> - if (!random_seed)
> - random_seed = local_tick ^ getpid (); /* Old racey fallback method */
> -}
> -
> /* Obtain the random_seed. Unless NOINIT, initialize it if
> it's not provided in the command line. */
>
> HOST_WIDE_INT
> get_random_seed (bool noinit)
> {
> - if (!flag_random_seed && !noinit)
> - init_random_seed ();
> + if (!random_seed && !noinit)
> + {
> + int fd = open ("/dev/urandom", O_RDONLY);
> + if (fd >= 0)
> + {
> + if (read (fd, &random_seed, sizeof (random_seed))
> + != sizeof (random_seed))
> + random_seed = 0;
> + close (fd);
> + }
> + if (!random_seed)
> + random_seed = local_tick ^ getpid ();
> + }
> return random_seed;
> }
>
> -/* Modify the random_seed string to VAL. Return its previous
> - value. */
> +/* Set flag_random_seed to VAL, and if non-null, reinitialize random_seed.
> */
>
> -const char *
> +void
> set_random_seed (const char *val)
> {
> - const char *old = flag_random_seed;
> flag_random_seed = val;
> if (flag_random_seed)
> {
> @@ -318,7 +304,6 @@ set_random_seed (const char *val)
> if (!(endp > flag_random_seed && *endp == 0))
> random_seed = crc32_string (0, flag_random_seed);
> }
> - return old;
> }
>
> /* Handler for fatal signals, such as SIGSEGV. These are transformed
> @@ -818,11 +803,6 @@ print_switch_values (print_switch_fn_type print_fn)
> int pos = 0;
> size_t j;
>
> - /* Fill in the -frandom-seed option, if the user didn't pass it, so
> - that it can be printed below. This helps reproducibility. */
> - if (!flag_random_seed)
> - init_random_seed ();
> -
> /* Print the options as passed. */
> pos = print_single_switch (print_fn, pos,
> SWITCH_TYPE_DESCRIPTIVE, _("options passed: "));
> diff --git a/gcc/toplev.h b/gcc/toplev.h
> index 2f6b587d233..aed806eb28f 100644
> --- a/gcc/toplev.h
> +++ b/gcc/toplev.h
> @@ -91,7 +91,7 @@ extern bool set_src_pwd (const char *);
> /* Functions used to manipulate the random seed. */
>
> extern HOST_WIDE_INT get_random_seed (bool);
> -extern const char *set_random_seed (const char *);
> +extern void set_random_seed (const char *);
>
> extern void initialize_rtl (void);
>
