proccontrol: make -s require a target

Require a command to exec or a pid to target and update usage and the
manpage to make this more clear.

It makes no sense to invoke a procctl(2) command on the current process
only to exit.  Users are sometimes confused about how proccontrol works
and think it effects their shell environment when invoked without a
target.  Disallowing this nonsensical behavior and clarifiying usage
will hopefully reduce confusion.

Reviewed by:	kib
Differential Revision:	https://reviews.freebsd.org/D46422

usr.bin/proccontrol/proccontrol.1

@@ -34,9 +34,12 @@
 .Sh SYNOPSIS
 .Nm
 .Fl m Ar mode
-.Op Fl s Ar control
-.Op Fl q
+.Fl s Ar control
 .Fl p Ar pid | command
+.Nm
+.Fl m Ar mode
+.Fl q
+.Op Fl p Ar pid | command
 .Sh DESCRIPTION
 The
 .Nm

usr.bin/proccontrol/proccontrol.c

@@ -81,10 +81,14 @@ str2pid(const char *str)
 static void __dead2
 usage(void)
 {
-
-	fprintf(stderr, "Usage: proccontrol -m (aslr|protmax|trace|trapcap|"
-	    "stackgap|nonewprivs|wxmap"KPTI_USAGE LA_USAGE") [-q] "
-	    "[-s (enable|disable)] [-p pid | command]\n");
+	fprintf(stderr, "Usage:\n");
+	fprintf(stderr, "    proccontrol -m mode -s (enable|disable) "
+	    "(-p pid | command)\n");
+	fprintf(stderr, "    proccontrol -m mode -q [-p pid]\n");
+	fprintf(stderr, "Modes: "
+	    "aslr|protmax|trace|trapcap|stackgap|nonewprivs|wxmap"
+	    KPTI_USAGE LA_USAGE
+	    "\n");
 	exit(1);
 }
 
@@ -157,6 +161,8 @@ main(int argc, char *argv[])
 			usage();
 		pid = getpid();
 	} else if (pid == -1) {
+		if (!query)
+			usage();
 		pid = getpid();
 	}