Re: [RFA/Ada] guard against a malloc failure

[Jerome Guitton <guitton at adacore dot com>]

Joel Brobecker (brobecker@adacore.com):

> > 2008-11-27  Jerome Guitton  <guitton@adacore.com>
> > 
> > 	* ada-lang.c (ada_template_to_fixed_record_type_1): Check size
> >         of type to guard against a crash.
> 
> Jerome and I just discussed this patch today, and we think we may
> have a better solution. Standby...

Right. It is possible to rewrite ada_template_to_fixed_record_type_1
to avoid the crash; the discriminant value is allocated using the type
being built; the crash may happen when a bogus dynamic field is
included to this partial type. The trick is to allocate the value
before any of these dynamic fields is added to the partial type.  When
we encounter a dynamic field, all the discriminant fields have already
been added, so it should be fine.

Here is the new patch, tested on linux. OK to apply?

2008-12-12  Jerome Guitton  <guitton@adacore.com>

	* ada-lang.c (ada_template_to_fixed_record_type_1): Allocate dval
	before a dynamic field is added. 

--- ada-lang.c.prev	2008-12-12 12:49:31.000000000 +0100
+++ ada-lang.c	2008-12-12 12:54:17.000000000 +0100
@@ -6831,7 +6831,7 @@ ada_template_to_fixed_record_type_1 (str
                                      int keep_dynamic_fields)
 {
   struct value *mark = value_mark ();
-  struct value *dval;
+  struct value *dval = dval0;
   struct type *rtype;
   int nfields, bit_len;
   int variant_field;
@@ -6882,10 +6882,17 @@ ada_template_to_fixed_record_type_1 (str
         }
       else if (is_dynamic_field (type, f))
         {
-          if (dval0 == NULL)
+          /* If dval is NULL, build it using the record type that we are
+             initializing. This takes advantage of the fact that the
+             discrimant fields should appear before any dynamic field;
+             so, at this point, the discriminant fields have already been
+             added to rtype. This property also assure that this dval will
+             be valid for the rest of the computation, no need to re-allocate
+             a new one for every dynamic field. Finally, as the value is
+             allocated before any  dynamic field has been added to the type,
+             we do not have to check its size before the allocation.  */
+          if (dval == NULL)
             dval = value_from_contents_and_address (rtype, valaddr, address);
-          else
-            dval = dval0;
 
           /* Get the fixed type of the field. Note that, in this case, we
              do not want to get the real type out of the tag: if the current
@@ -6931,10 +6938,8 @@ ada_template_to_fixed_record_type_1 (str
 
       off = TYPE_FIELD_BITPOS (rtype, variant_field);
 
-      if (dval0 == NULL)
+      if (dval == NULL)
         dval = value_from_contents_and_address (rtype, valaddr, address);
-      else
-        dval = dval0;
 
       branch_type =
         to_fixed_variant_branch_type