ash: improve expandstr()

The dash maintainer recently posted a fix for issues with expanding
PS1.  These had already been fixed differently in BusyBox ash.  Borrow
a couple of improvements:

- Use a single call to setjmp() to trap errors in both readtoken1()
  and expandarg().

- In case of error set the prompt to the literal value of PS1 rather
  than the half-digested nonsense in stackblock() which might include
  ugly control characters.

function                                             old     new   delta
expandstr                                            353     300     -53

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

1 files changed, 21 insertions, 20 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 4b5eafa7c..d6040f47e 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -13098,29 +13098,27 @@ expandstr(const char *ps, int syntax_type)
         volatile int saveint;
         struct jmploc *volatile savehandler = exception_handler;
         struct jmploc jmploc;
+        const char *volatile result;
+        int err;
 
         /* XXX Fix (char *) cast. */
         setinputstring((char *)ps);
 
         saveprompt = doprompt;
         doprompt = 0;
+        result = ps;
+
+        SAVE_INT(saveint);
+        err = setjmp(jmploc.loc);
+        if (err)
+                goto out;
 
         /* readtoken1() might die horribly.
          * Try a prompt with syntactically wrong command:
          * PS1='$(date "+%H:%M:%S) > '
          */
-        SAVE_INT(saveint);
-        if (setjmp(jmploc.loc) == 0) {
-                exception_handler = &jmploc;
-                readtoken1(pgetc(), syntax_type, FAKEEOFMARK, 0);
-        }
-        exception_handler = savehandler;
-        RESTORE_INT(saveint);
-
-        doprompt = saveprompt;
-
-        /* Try: PS1='`xxx(`' */
-        unwindfiles(file_stop);
+        exception_handler = &jmploc;
+        readtoken1(pgetc(), syntax_type, FAKEEOFMARK, 0);
 
         n.narg.type = NARG;
         n.narg.next = NULL;
@@ -13130,17 +13128,20 @@ expandstr(const char *ps, int syntax_type)
         /* expandarg() might fail too:
          * PS1='$((123+))'
          */
-        SAVE_INT(saveint);
-        if (setjmp(jmploc.loc) == 0) {
-                exception_handler = &jmploc;
-                expandarg(&n, NULL, EXP_QUOTED);
-        } else if (exception_type == EXEXIT) {
-                exitshell();
-        }
+        expandarg(&n, NULL, EXP_QUOTED);
+        result = stackblock();
+
+out:
         exception_handler = savehandler;
+        if (err && exception_type != EXERROR)
+                longjmp(exception_handler->loc, 1);
         RESTORE_INT(saveint);
 
-        return stackblock();
+        doprompt = saveprompt;
+        /* Try: PS1='`xxx(`' */
+        unwindfiles(file_stop);
+
+        return result;
 }
 
 static inline int