Add support for dynamic type lengths

In Ada, a type with variant parts can have a variable length.  This
patch adds support for this to gdb, by integrating the length
computation into the dynamic type resolution code.

gdb/ChangeLog
2020-04-24  Tom Tromey  <tromey@adacore.com>

	* dwarf2/read.c (read_structure_type): Handle dynamic length.
	* gdbtypes.c (is_dynamic_type_internal): Check
	TYPE_HAS_DYNAMIC_LENGTH.
	(resolve_dynamic_type_internal): Use TYPE_DYNAMIC_LENGTH.
	* gdbtypes.h (TYPE_HAS_DYNAMIC_LENGTH, TYPE_DYNAMIC_LENGTH):
	New macros.
	(enum dynamic_prop_node_kind) <DYN_PROP_BYTE_SIZE>: New
	constant.

gdb/testsuite/ChangeLog
2020-04-24  Tom Tromey  <tromey@adacore.com>

	* gdb.ada/variant.exp: New file
	* gdb.ada/variant/pkg.adb: New file
	* gdb.ada/variant/pck.adb: New file

1 files changed, 4 insertions, 8 deletions

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index dd808e0..f6d0624 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -15300,14 +15300,10 @@ read_structure_type (struct die_info *die, struct dwarf2_cu *cu)
         TYPE_LENGTH (type) = DW_UNSND (attr);
       else
 	{
-	  /* For the moment, dynamic type sizes are not supported
-	     by GDB's struct type.  The actual size is determined
-	     on-demand when resolving the type of a given object,
-	     so set the type's length to zero for now.  Otherwise,
-	     we record an expression as the length, and that expression
-	     could lead to a very large value, which could eventually
-	     lead to us trying to allocate that much memory when creating
-	     a value of that type.  */
+	  struct dynamic_prop prop;
+	  if (attr_to_dynamic_prop (attr, die, cu, &prop,
+				    cu->per_cu->addr_type ()))
+	    add_dyn_prop (DYN_PROP_BYTE_SIZE, prop, type);
           TYPE_LENGTH (type) = 0;
 	}
     }