sh: Do not run callers' exception handlers in subshells.

Reset the exception handler in the child to main's.

This avoids inappropriate double cleanups or shell duplication when the
exception is caught, such as 'fc' and future 'command eval' and 'command .'.

bin/sh/jobs.c

@@ -757,6 +757,7 @@ forkshell(struct job *jp, union node *n, int mode)
 		TRACE(("Child shell %d\n", (int)getpid()));
 		wasroot = rootshell;
 		rootshell = 0;
+		handler = &main_handler;
 		closescript();
 		INTON;
 		clear_traps();

bin/sh/main.c

@@ -75,6 +75,7 @@ __FBSDID("$FreeBSD$");
 
 int rootpid;
 int rootshell;
+struct jmploc main_handler;
 
 STATIC void read_profile(char *);
 STATIC char *find_dot_file(char *);
@@ -90,14 +91,13 @@ STATIC char *find_dot_file(char *);
 int
 main(int argc, char *argv[])
 {
-	struct jmploc jmploc;
 	struct stackmark smark;
 	volatile int state;
 	char *shinit;
 
 	(void) setlocale(LC_ALL, "");
 	state = 0;
-	if (setjmp(jmploc.loc)) {
+	if (setjmp(main_handler.loc)) {
 		/*
 		 * When a shell procedure is executed, we raise the
 		 * exception EXSHELLPROC to clean up before executing
@@ -143,7 +143,7 @@ main(int argc, char *argv[])
 		else
 			goto state4;
 	}
-	handler = &jmploc;
+	handler = &main_handler;
 #ifdef DEBUG
 	opentrace();
 	trputs("Shell args:  ");  trargs(argv);

bin/sh/main.h

@@ -35,6 +35,7 @@
 
 extern int rootpid;	/* pid of main shell */
 extern int rootshell;	/* true if we aren't a child of the main shell */
+extern struct jmploc main_handler;	/* top level exception handler */
 
 void readcmdfile(const char *);
 void cmdloop(int);

tools/regression/bin/sh/builtins/fc2.0

@@ -0,0 +1,34 @@
+# $FreeBSD$
+set -e
+trap 'echo Broken pipe -- test failed' pipe
+
+P=${TMPDIR:-/tmp}
+cd $P
+T=$(mktemp -d sh-test.XXXXXX)
+cd $T
+
+mkfifo input output error
+HISTFILE=/dev/null sh +m -i <input >output 2>error &
+exec 3>input
+{
+	# Command not found, containing slash
+	echo '/var/empty/nonexistent' >&3
+	# Read error message, shell will read new input now
+	read dummy <&5
+	# Execute bad command again
+	echo 'fc -e true; echo continued' >&3
+	read dummy <&5
+	read line <&4 && [ "$line" = continued ] && : ${rc:=0}
+	exec 3>&-
+	# Old sh duplicates itself after the fc, producing another line
+	# of output.
+	if read line <&4; then
+		echo "Extraneous output: $line"
+		rc=1
+	fi
+} 4<output 5<error
+exec 3>&-
+
+rm input output error
+rmdir ${P}/${T}
+exit ${rc:-3}