misc: fix ggc-7 fallthrough warnings

(Original patch and commit message edited by Rudi.)

gcc-7 adds -Wimplicit-fallthrough=3 to our default flag -Wextra.
This warning can be silenced by using comment /* fallthrough */
which is also recognized by other tools like coverity. There are
also other valid comments (see man gcc-7) but we consolidate this
style now.

We could have also used __attribute__((fallthrough)) but the comment
looks nice and does not need to be ifdef'ed for compatibility.

Reference: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=7652
Reference: https://developers.redhat.com/blog/2017/03/10/wimplicit-fallthrough-in-gcc-7/
Reviewed-by: Ruediger Meier <ruediger.meier@ga-group.nl>
Suggested-by: Karel Zak <kzak@redhat.com>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>

disk-utils/mkfs.cramfs.c

@@ -123,7 +123,7 @@ struct entry {
 #define CRAMFS_OFFSET_WIDTH 26
 
 /* Input status of 0 to print help and exit without an error. */
-static void
+static void __attribute__((__noreturn__))
 usage(int status) {
 	FILE *stream = status ? stderr : stdout;
 

login-utils/last.c

@@ -830,7 +830,7 @@ static void process_wtmp_file(const struct last_control *ctl,
 					c = whydown;
 				quit = list(ctl, &ut, lastboot, c);
 			}
-			/* FALLTHRU */
+			/* fallthrough */
 
 		case DEAD_PROCESS:
 			/*

login-utils/su-common.c

@@ -899,6 +899,7 @@ su_main (int argc, char **argv, int mode)
     /* fallthrough if -u <user> is not specified, then follow
      * traditional su(1) behavior
      */
+     /* fallthrough */
   case SU_MODE:
     if (optind < argc)
       new_user = argv[optind++];

login-utils/sulogin.c

@@ -267,11 +267,11 @@ static void tcfinal(struct console *con)
 		break;
 	case 1:				/* odd parity */
 		tio->c_cflag |= PARODD;
-		/* fall through */
+		/* fallthrough */
 	case 2:				/* even parity */
 		tio->c_cflag |= PARENB;
 		tio->c_iflag |= (INPCK | ISTRIP);
-		/* fall through */
+		/* fallthrough */
 	case (1 | 2):			/* no parity bit */
 		tio->c_cflag &= ~CSIZE;
 		tio->c_cflag |= CS7;
@@ -971,7 +971,6 @@ int main(int argc, char **argv)
 		switch ((con->pid = fork())) {
 		case 0:
 			mask_signal(SIGCHLD, SIG_DFL, NULL);
-			/* fall through */
 		nofork:
 			setup(con);
 			while (1) {
@@ -1024,7 +1023,7 @@ int main(int argc, char **argv)
 			exit(0);
 		case -1:
 			warn(_("fork failed"));
-			/* fall through */
+			/* fallthrough */
 		default:
 			break;
 		}

misc-utils/cal.c

@@ -431,7 +431,7 @@ int main(int argc, char **argv)
 		ctl.req.day = strtos32_or_err(*argv++, _("illegal day value"));
 		if (ctl.req.day < 1 || DAYS_IN_MONTH < ctl.req.day)
 			errx(EXIT_FAILURE, _("illegal day value: use 1-%d"), DAYS_IN_MONTH);
-		/* FALLTHROUGH */
+		/* fallthrough */
 	case 2:
 		if (isdigit(**argv))
 			ctl.req.month = strtos32_or_err(*argv++, _("illegal month value: use 1-12"));
@@ -443,7 +443,7 @@ int main(int argc, char **argv)
 		}
 		if (ctl.req.month < 1 || MONTHS_IN_YEAR < ctl.req.month)
 			errx(EXIT_FAILURE, _("illegal month value: use 1-12"));
-		/* FALLTHROUGH */
+		/* fallthrough */
 	case 1:
 		ctl.req.year = strtos32_or_err(*argv++, _("illegal year value"));
 		if (ctl.req.year < SMALLEST_YEAR)

misc-utils/rename.c

@@ -189,7 +189,6 @@ int main(int argc, char **argv)
 			return EXIT_SUCCESS;
 		case 'h':
 			usage(stdout);
-			/* fallthrough */
 		default:
 			errtryhelp(EXIT_FAILURE);
 		}

sys-utils/flock.c

@@ -305,7 +305,7 @@ int main(int argc, char *argv[])
 				if (open_flags & O_RDWR)
 					break;
 			}
-			/* go through */
+			/* fallthrough */
 		default:
 			/* Other errors */
 			if (filename)

sys-utils/hwclock.c

@@ -1209,7 +1209,8 @@ static void out_version(void)
  * fmt, ... ), show a usage information and terminate the program
  * afterwards.
  */
-static void usage(const struct hwclock_control *ctl, const char *fmt, ...)
+static void __attribute__((__noreturn__))
+usage(const struct hwclock_control *ctl, const char *fmt, ...)
 {
 	FILE *usageto;
 	va_list ap;

sys-utils/ipcrm.c

@@ -346,6 +346,7 @@ int main(int argc, char **argv)
 				ret++;
 				break;
 			}
+			/* fallthrough */
 		case 'm':
 			if (!iskey)
 				id = strtos32_or_err(optarg, _("failed to parse argument"));
@@ -359,6 +360,7 @@ int main(int argc, char **argv)
 				ret++;
 				break;
 			}
+			/* fallthrough */
 		case 'q':
 			if (!iskey)
 				id = strtos32_or_err(optarg, _("failed to parse argument"));
@@ -372,6 +374,7 @@ int main(int argc, char **argv)
 				ret++;
 				break;
 			}
+			/* fallthrough */
 		case 's':
 			if (!iskey)
 				id = strtos32_or_err(optarg, _("failed to parse argument"));

sys-utils/nsenter.c

@@ -65,7 +65,7 @@ static struct namespace_file {
 	{ .nstype = 0, .name = NULL, .fd = -1 }
 };
 
-static void usage(int status)
+static void __attribute__((__noreturn__)) usage(int status)
 {
 	FILE *out = status == EXIT_SUCCESS ? stdout : stderr;
 

sys-utils/unshare.c

@@ -238,7 +238,7 @@ static void bind_ns_files_from_child(pid_t *child, int fds[2])
 	}
 }
 
-static void usage(int status)
+static void __attribute__((__noreturn__)) usage(int status)
 {
 	FILE *out = status == EXIT_SUCCESS ? stdout : stderr;
 

term-utils/agetty.c

@@ -2041,12 +2041,12 @@ static void termio_final(struct options *op, struct termios *tp, struct chardata
 	case 1:
 		/* odd parity */
 		tp->c_cflag |= PARODD;
-		/* do not break */
+		/* fallthrough */
 	case 2:
 		/* even parity */
 		tp->c_cflag |= PARENB;
 		tp->c_iflag |= INPCK | ISTRIP;
-		/* do not break */
+		/* fallthrough */
 	case (1 | 2):
 		/* no parity bit */
 		tp->c_cflag &= ~CSIZE;

text-utils/hexdump-parse.c

@@ -351,7 +351,7 @@ isint:				cs[3] = '\0';
 					case 'A':
 						endfu = fu;
 						fu->flags |= F_IGNORE;
-						/* FALLTHROUGH */
+						/* fallthrough */
 					case 'a':
 						pr->flags = F_ADDRESS;
 						++p2;

text-utils/more.c

@@ -1270,7 +1270,7 @@ int command(char *filename, register FILE *f)
 				break;
 			}
 			lastp++;
-			/* fall through */
+			/* fallthrough */
 		case '/':
 			if (nlines == 0)
 				nlines++;
@@ -1368,7 +1368,7 @@ int command(char *filename, register FILE *f)
 						(char *)0);
 				break;
 			}
-			/* fall through */
+			/* fallthrough */
 		default:
 			if (dum_opt) {
 				kill_line();
@@ -2023,6 +2023,7 @@ int expand(char **outbuf, char *inbuf)
 				*outstr++ = *inpstr++;
 				break;
 			}
+			/* fallthrough */
 		default:
 			*outstr++ = c;
 		}

text-utils/pg.c

@@ -659,7 +659,7 @@ static void prompt(long long pageno)
 					break;
 				case SEARCH_FIN:
 					state = SEARCH;
-					/* FALLTHRU */
+					/* fallthrough */
 				case SEARCH:
 					if (cmd.cmdline[cmd.cmdlen - 1] == '\\') {
 						escape = 1;
@@ -738,7 +738,7 @@ static void prompt(long long pageno)
 					continue;
 				}
 				state = COUNT;
-				/* FALLTHRU */
+				/* fallthrough */
 			case COUNT:
 				break;
 			case ADDON_FIN:

text-utils/ul.c

@@ -208,7 +208,7 @@ int main(int argc, char **argv)
 
 	default:
 		warnx(_("trouble reading terminfo"));
-		/* fall through to ... */
+		/* fallthrough */
 
 	case 0:
 		if (tflag)
@@ -317,7 +317,7 @@ static void filter(FILE *f)
 			}
 			obuf[col].c_char = '_';
 			obuf[col].c_width = 1;
-			/* fall through */
+			/* fallthrough */
 		case ' ':
 			setcol(col + 1);
 			continue;