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?
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);
