libbb: consolidate NOMMU fix of restoring high bit in argv[0][0]

function                                             old     new   delta
fork_or_rexec                                         46      56     +10
bootchartd_main                                     1087    1079      -8
cpio_main                                            674     661     -13
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/2 up/down: 10/-21)            Total: -11 bytes

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

archival/cpio.c

@@ -504,7 +504,6 @@ int cpio_main(int argc UNUSED_PARAM, char **argv)
 			goto dump;
 		}
 		/* parent */
-		USE_FOR_NOMMU(argv[-optind][0] &= 0x7f); /* undo fork_or_rexec() damage */
 		xchdir(*argv++);
 		close(pp.wr);
 		xmove_fd(pp.rd, STDIN_FILENO);

include/libbb.h

@@ -1319,7 +1319,7 @@ enum {
 # define bb_daemonize(flags)                bb_daemonize_or_rexec(flags, bogus)
 #else
   extern bool re_execed;
-  /* Note: re_exec() and fork_or_rexec() do argv[0][0] |= 0x80 on NOMMU!
+  /* Note: re_exec() sets argv[0][0] |= 0x80 on NOMMU!
    * _Parent_ needs to undo it if it doesn't want to have argv[0] mangled.
    */
   void re_exec(char **argv) NORETURN FAST_FUNC;

init/bootchartd.c

@@ -435,8 +435,6 @@ int bootchartd_main(int argc UNUSED_PARAM, char **argv)
 
 	/* parent */
 
-	USE_FOR_NOMMU(argv[0][0] &= 0x7f); /* undo fork_or_rexec() damage */
-
 	if (DO_SIGNAL_SYNC) {
 		/* Wait for logger child to set handlers, then unpause it.
 		 * Otherwise with short-lived PROG (e.g. "bootchartd start true")

libbb/vfork_daemon_rexec.c

@@ -268,10 +268,12 @@ pid_t FAST_FUNC fork_or_rexec(char **argv)
 	/* fflush_all(); ? - so far all callers had no buffered output to flush */
 
 	pid = xvfork();
-	if (pid) /* parent */
-		return pid;
-	/* child - re-exec ourself */
-	re_exec(argv);
+	if (pid == 0) /* child - re-exec ourself */
+		re_exec(argv); /* NORETURN */
+
+	/* parent */
+	argv[0][0] &= 0x7f; /* undo re_rexec() damage */
+	return pid;
 }
 #endif
 

networking/httpd.c

@@ -2713,8 +2713,8 @@ static void mini_httpd_nommu(int server_socket, int argc, char **argv)
 			/* Run a copy of ourself in inetd mode */
 			re_exec(argv_copy);
 		}
-		argv_copy[0][0] &= 0x7f;
 		/* parent, or vfork failed */
+		argv_copy[0][0] &= 0x7f; /* undo re_rexec() damage */
 		close(n);
 	} /* while (1) */
 	/* never reached */