*: stop using atexit in non-debug build: saves ~260 in bss with musl

"builtin" below is atexit's 32-element global array of functions to call.

function                                             old     new   delta
top_main                                             879     889     +10
launch_helper                                        185     193      +8
powertop_main                                       1555    1559      +4
sed_main                                             651     650      -1
slot                                                   4       -      -4
call                                                   4       -      -4
atexit                                                23       -     -23
kill_helper                                           31       -     -31
__funcs_on_exit                                      120       -    -120
__cxa_atexit                                         168       -    -168
builtin                                              260       -    -260
------------------------------------------------------------------------------
(add/remove: 0/8 grow/shrink: 3/1 up/down: 22/-611)          Total: -589 bytes
   text	   data	    bss	    dec	    hex	filename
 912364	    563	   6132	 919059	  e0613	busybox_old
 912035	    563	   5844	 918442	  e03aa	busybox_unstripped

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

editors/sed.c

@@ -1521,7 +1521,7 @@ int sed_main(int argc UNUSED_PARAM, char **argv)
 	//argc -= optind;
 	argv += optind;
 	if (opt & OPT_in_place) { // -i
-		atexit(cleanup_outname);
+		die_func = cleanup_outname;
 	}
 	if (opt & (2|4))
 		G.regex_type |= REG_EXTENDED; // -r or -E

mailutils/mail.c

@@ -6,23 +6,15 @@
  *
  * Licensed under GPLv2, see file LICENSE in this source tree.
  */
+#include <sys/prctl.h>
 #include "libbb.h"
 #include "mail.h"
 
-static void kill_helper(void)
-{
-	if (G.helper_pid > 0) {
-		kill(G.helper_pid, SIGTERM);
-		G.helper_pid = 0;
-	}
-}
-
 // generic signal handler
 static void signal_handler(int signo)
 {
 #define err signo
 	if (SIGALRM == signo) {
-		kill_helper();
 		bb_error_msg_and_die("timed out");
 	}
 
@@ -66,16 +58,15 @@ void FAST_FUNC launch_helper(const char **argv)
 	// child stdout [1] -> parent stdin [0]
 
 	if (!G.helper_pid) {
-		// child: try to execute connection helper
+		// child
+		// if parent dies, get SIGTERM
+		prctl(PR_SET_PDEATHSIG, SIGTERM, 0, 0, 0);
+		// try to execute connection helper
 		// NB: SIGCHLD & SIGALRM revert to SIG_DFL on exec
 		BB_EXECVP_or_die((char**)argv);
 	}
 
-	// parent
+	// parent goes on
-	// check whether child is alive
-	//redundant:signal_handler(SIGCHLD);
-	// child seems OK -> parent goes on
-	atexit(kill_helper);
 }
 
 char* FAST_FUNC send_mail_command(const char *fmt, const char *param)

procps/powertop.c

@@ -8,11 +8,6 @@
  *
  * Licensed under GPLv2, see file LICENSE in this source tree.
  */
-
-//applet:IF_POWERTOP(APPLET(powertop, BB_DIR_USR_SBIN, BB_SUID_DROP))
-
-//kbuild:lib-$(CONFIG_POWERTOP) += powertop.o
-
 //config:config POWERTOP
 //config:	bool "powertop (9.1 kb)"
 //config:	default y
@@ -27,6 +22,10 @@
 //config:	Without this, powertop will only refresh display every 10 seconds.
 //config:	No keyboard commands will work, only ^C to terminate.
 
+//applet:IF_POWERTOP(APPLET(powertop, BB_DIR_USR_SBIN, BB_SUID_DROP))
+
+//kbuild:lib-$(CONFIG_POWERTOP) += powertop.o
+
 // XXX This should be configurable
 #define ENABLE_FEATURE_POWERTOP_PROCIRQ 1
 
@@ -718,7 +717,7 @@ int powertop_main(int UNUSED_PARAM argc, char UNUSED_PARAM **argv)
 	set_termios_to_raw(STDIN_FILENO, &G.init_settings, TERMIOS_CLEAR_ISIG);
 	bb_signals(BB_FATAL_SIGS, sig_handler);
 	/* So we don't forget to reset term settings */
-	atexit(reset_term);
+	die_func = reset_term;
 #endif
 
 	/* Collect initial data */
@@ -855,6 +854,9 @@ int powertop_main(int UNUSED_PARAM argc, char UNUSED_PARAM **argv)
 	} /* for (;;) */
 
 	bb_putchar('\n');
+#if ENABLE_FEATURE_POWERTOP_INTERACTIVE
+	reset_term();
+#endif
 
 	return EXIT_SUCCESS;
 }

procps/top.c

@@ -1146,6 +1146,7 @@ int top_main(int argc UNUSED_PARAM, char **argv)
 	else {
 		/* Turn on unbuffered input; turn off echoing, ^C ^Z etc */
 		set_termios_to_raw(STDIN_FILENO, &initial_settings, TERMIOS_CLEAR_ISIG);
+		die_func = reset_term;
 	}
 
 	bb_signals(BB_FATAL_SIGS, sig_catcher);