[RFA] (display_uses_solib_p): Redo loop, scan element list backwards.

[dje at google dot com (Doug Evans)]

Hi.

I noticed sigbpt.exp is failing.
I was getting a "Value out of range" error inside display_uses_solib_p.
I traced it to the expression elements array being referenced out of bounds.

I think this patch is the right fix.
The expression elements array needs to be scanned backwards
when using operator_length: it examines the element at the _end_
of the array.

Ok to check in?

2009-03-17  Doug Evans  <dje@google.com>

	* printcmd.c (display_uses_solib_p): Redo loop, scan element list
	backwards.

Index: printcmd.c
===================================================================
RCS file: /cvs/src/src/gdb/printcmd.c,v
retrieving revision 1.147
diff -u -p -r1.147 printcmd.c
--- printcmd.c	9 Mar 2009 22:38:37 -0000	1.147
+++ printcmd.c	18 Mar 2009 04:28:26 -0000
@@ -1763,18 +1763,23 @@ static int
 display_uses_solib_p (const struct display *d,
 		      const struct so_list *solib)
 {
-  int i;
+  int endpos;
   struct expression *const exp = d->exp;
+  union exp_element *const elts = exp->elts;
 
   if (d->block != NULL
       && solib_contains_address_p (solib, d->block->startaddr))
     return 1;
 
-  for (i = 0; i < exp->nelts; )
+  for (endpos = exp->nelts; endpos > 0; )
     {
-      int args, oplen = 0;
-      const union exp_element *const elts = exp->elts;
+      int i, args, oplen = 0;
 
+      exp->language_defn->la_exp_desc->operator_length (exp, endpos,
+							&oplen, &args);
+      gdb_assert (oplen > 0);
+
+      i = endpos - oplen;
       if (elts[i].opcode == OP_VAR_VALUE)
 	{
 	  const struct block *const block = elts[i + 1].block;
@@ -1789,11 +1794,9 @@ display_uses_solib_p (const struct displ
 	  if (section && section->objfile == solib->objfile)
 	    return 1;
 	}
-      exp->language_defn->la_exp_desc->operator_length (exp, i + 1,
-							&oplen, &args);
-      gdb_assert (oplen > 0);
-      i += oplen;
+      endpos -= oplen;
     }
+
   return 0;
 }