Use getentropy() for seeding PRNG

The getentropy function, found on Linux, OpenBSD, and recently also
FreeBSD, can be used to get random bytes to initialize the PRNG.  It
is similar to the traditional way of reading from /dev/urandom, but
being a system call rather than a special file, it doesn't suffer from
problems like running out of file descriptors, or failure when running
in a container where /dev/urandom may not be available.

Regtested on x86_64-pc-linux-gnu, Ok for trunk?

2018-08-13  Janne Blomqvist  <jb@gcc.gnu.org>

	* configure.ac: Check for getentropy.
	* intrinsics/random.c (getosrandom): Use getentropy if available.
	* config.h.in: Regenerated.
	* configure: Regenerated.

From-SVN: r263522

libgfortran/ChangeLog

+2018-08-13  Janne Blomqvist  <jb@gcc.gnu.org>
+
+	* configure.ac: Check for getentropy.
+	* intrinsics/random.c (getosrandom): Use getentropy if available.
+	* config.h.in: Regenerated.
+	* configure: Regenerated.
+
 2018-07-31  Andre Vieira  <andre.simoesdiasvieira@arm.com>
 
 	Revert 'AsyncI/O patch committed'

libgfortran/config.h.in

@@ -453,6 +453,9 @@
 /* Define to 1 if you have the `getegid' function. */
 #undef HAVE_GETEGID
 
+/* Define to 1 if you have the `getentropy' function. */
+#undef HAVE_GETENTROPY
+
 /* Define to 1 if you have the `geteuid' function. */
 #undef HAVE_GETEUID
 

libgfortran/configure

@@ -2570,6 +2570,7 @@ as_fn_append ac_func_list " snprintf"
 as_fn_append ac_func_list " ftruncate"
 as_fn_append ac_func_list " chsize"
 as_fn_append ac_func_list " chdir"
+as_fn_append ac_func_list " getentropy"
 as_fn_append ac_func_list " getlogin"
 as_fn_append ac_func_list " gethostname"
 as_fn_append ac_func_list " kill"
@@ -12512,7 +12513,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 12515 "configure"
+#line 12516 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -12618,7 +12619,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 12621 "configure"
+#line 12622 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -16778,6 +16779,8 @@ done
 
 
 
+
+
 fi
 
 # Check strerror_r, cannot be above as versions with two and three arguments exist

libgfortran/configure.ac

@@ -312,7 +312,8 @@ if test "${hardwire_newlib:-0}" -eq 1; then
    fi
 else
    AC_CHECK_FUNCS_ONCE(getrusage times mkstemp strtof strtold snprintf \
-   ftruncate chsize chdir getlogin gethostname kill link symlink sleep ttyname \
+   ftruncate chsize chdir getentropy getlogin gethostname kill link symlink \
+   sleep ttyname \
    alarm access fork setmode fcntl \
    gettimeofday stat fstat lstat getpwuid vsnprintf dup \
    getcwd localtime_r gmtime_r getpwuid_r ttyname_r clock_gettime \

libgfortran/intrinsics/random.c

@@ -310,11 +310,10 @@ getosrandom (void *buf, size_t buflen)
     rand_s (&b[i]);
   return buflen;
 #else
-  /*
-     TODO: When glibc adds a wrapper for the getrandom() system call
-     on Linux, one could use that.
-
-     TODO: One could use getentropy() on OpenBSD.  */
+#ifdef HAVE_GETENTROPY
+  if (getentropy (buf, buflen) == 0)
+    return 0;
+#endif
   int flags = O_RDONLY;
 #ifdef O_CLOEXEC
   flags |= O_CLOEXEC;