[Ada] Better handling of dynamic types in ada_value_primitive_packed_val

There is some partial handling for dynamic types in
ada_value_primitive_packed_val, but this support was added
in a fairly ad hoc way, and actually only covered the situation
where OBJ is not NULL and its contents had not been fetched yet.
In addition, even in the cases that it does cover, it doesn't make
much sense. In particular, it was adjusting BIT_SIZE and SRC_LEN,
which are properties of the data to be extracted _from_, based
on TYPE's length once resolved, which is a property of the data
we want to extract _to_.

This patch hopefully adjust this function to handle dynamic types
correctly, and in all cases. It does so by unpacking the data into
a temporary buffer in order to use that buffer to resolve the type.
And _then_ creates the resulting value from that resolved type.

gdb/ChangeLog:

        * ada-lang.c (ada_value_primitive_packed_val): Rework handling
        of case where TYPE is dynamic.

2 files changed, 57 insertions, 29 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index a511592..06a0637 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,10 @@
 2015-10-09  Joel Brobecker  <brobecker@adacore.com>
 
+	* ada-lang.c (ada_value_primitive_packed_val): Rework handling
+	of case where TYPE is dynamic.
+
+2015-10-09  Joel Brobecker  <brobecker@adacore.com>
+
 	* ada-lang.c (ada_unpack_from_contents): New function,
 	extracted from ada_value_primitive_packed_val.
 	(ada_value_primitive_packed_val): Replace extracted out code
diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 6947d76..2b2c47c 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -2520,9 +2520,50 @@ ada_value_primitive_packed_val (struct value *obj, const gdb_byte *valaddr,
   int src_len = (bit_size + bit_offset + HOST_CHAR_BIT - 1) / 8;
   gdb_byte *unpacked;
   int is_scalar;
+  const int is_big_endian = gdbarch_bits_big_endian (get_type_arch (type));
+  gdb_byte *staging = NULL;
+  int staging_len = 0;
+  struct cleanup *old_chain = make_cleanup (null_cleanup, NULL);
 
   type = ada_check_typedef (type);
 
+  switch (TYPE_CODE (type))
+    {
+    case TYPE_CODE_ARRAY:
+    case TYPE_CODE_UNION:
+    case TYPE_CODE_STRUCT:
+      is_scalar = 0;
+      break;
+    default:
+      is_scalar = 1;
+      break;
+    }
+
+  if (obj == NULL)
+    src = (gdb_byte *) valaddr + offset;
+  else
+    src = (gdb_byte *) value_contents (obj) + offset;
+
+  if (is_dynamic_type (type))
+    {
+      /* The length of TYPE might by dynamic, so we need to resolve
+	 TYPE in order to know its actual size, which we then use
+	 to create the contents buffer of the value we return.
+	 The difficulty is that the data containing our object is
+	 packed, and therefore maybe not at a byte boundary.  So, what
+	 we do, is unpack the data into a byte-aligned buffer, and then
+	 use that buffer as our object's value for resolving the type.  */
+      staging_len = (bit_size + HOST_CHAR_BIT - 1) / HOST_CHAR_BIT;
+      staging = malloc (staging_len);
+      make_cleanup (xfree, staging);
+
+      ada_unpack_from_contents (src, bit_offset, bit_size,
+			        staging, staging_len,
+				is_big_endian, has_negatives (type),
+				is_scalar);
+      type = resolve_dynamic_type (type, staging, 0);
+    }
+
   if (obj == NULL)
     {
       v = allocate_value (type);
@@ -2531,18 +2572,6 @@ ada_value_primitive_packed_val (struct value *obj, const gdb_byte *valaddr,
   else if (VALUE_LVAL (obj) == lval_memory && value_lazy (obj))
     {
       v = value_at (type, value_address (obj) + offset);
-      type = value_type (v);
-      if (TYPE_LENGTH (type) * HOST_CHAR_BIT < bit_size)
-	{
-	  /* This can happen in the case of an array of dynamic objects,
-	     where the size of each element changes from element to element.
-	     In that case, we're initially given the array stride, but
-	     after resolving the element type, we find that its size is
-	     less than this stride.  In that case, adjust bit_size to
-	     match TYPE's length, and recompute LEN accordingly.  */
-	  bit_size = TYPE_LENGTH (type) * HOST_CHAR_BIT;
-	  src_len = TYPE_LENGTH (type) + (bit_offset + HOST_CHAR_BIT - 1) / 8;
-	}
       src = alloca (src_len);
       read_memory (value_address (v), src, src_len);
     }
@@ -2577,29 +2606,23 @@ ada_value_primitive_packed_val (struct value *obj, const gdb_byte *valaddr,
   if (bit_size == 0)
     {
       memset (unpacked, 0, TYPE_LENGTH (type));
+      do_cleanups (old_chain);
       return v;
     }
 
-  switch (TYPE_CODE (type))
+  if (staging != NULL && staging_len == TYPE_LENGTH (type))
     {
-    case TYPE_CODE_ARRAY:
-    case TYPE_CODE_UNION:
-    case TYPE_CODE_STRUCT:
-      is_scalar = 0;
-      break;
-    default:
-      is_scalar = 1;
-      break;
+      /* Small short-cut: If we've unpacked the data into a buffer
+	 of the same size as TYPE's length, then we can reuse that,
+	 instead of doing the unpacking again.  */
+      memcpy (unpacked, staging, staging_len);
     }
+  else
+    ada_unpack_from_contents (src, bit_offset, bit_size,
+			      unpacked, TYPE_LENGTH (type),
+			      is_big_endian, has_negatives (type), is_scalar);
 
-  ada_unpack_from_contents (src, bit_offset, bit_size,
-			    unpacked, TYPE_LENGTH (type),
-			    gdbarch_bits_big_endian (get_type_arch (type)),
-			    has_negatives (type), is_scalar);
-
-  if (is_dynamic_type (value_type (v)))
-    v = value_from_contents_and_address (value_type (v), value_contents (v),
-					 0);
+  do_cleanups (old_chain);
   return v;
 }