ash: prevent error in backquotes in PS1 from exiting shell

Setting PS1 to:

   PS1='`xxx(`'

causes the shell to terminate with the error:

   sh: syntax error: unexpected end of file (expecting ")")

This happens because old-style backquotes require the input to be reread
and thus call setinputstring() a second time.  Prevent the problem by
unwinding all recently opened files in expandstr().

function                                             old     new   delta
unwindfiles                                            -      22     +22
expandstr                                            247     262     +15
forkchild                                            631     625      -6
evalcommand                                         1694    1685      -9
ash_main                                            1346    1336     -10
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/3 up/down: 37/-25)             Total: 12 bytes

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/shell/ash.c b/shell/ash.c
index b707d00d0..f3a2c6952 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -13042,6 +13042,7 @@ expandstr(const char *ps, int syntax_type)
 {
         union node n;
         int saveprompt;
+        struct parsefile *file_stop = g_parsefile;
 
         /* XXX Fix (char *) cast. */
         setinputstring((char *)ps);
@@ -13068,7 +13069,8 @@ expandstr(const char *ps, int syntax_type)
 
         doprompt = saveprompt;
 
-        popfile();
+        /* Try: PS1='`xxx(`' */
+        unwindfiles(file_stop);
 
         n.narg.type = NARG;
         n.narg.next = NULL;