[PATCH] gdb: tighten assertions in set_type_vptr_*

[simon.marchi@polymtl.ca]

From: Simon Marchi <simon.marchi@polymtl.ca>

In C++, only structures and classes (represented by TYPE_CODE_STRUCT)
can participate in inheritance.  I therefore think it does not make
sense to allow for TYPE_CODE_UNION in set_type_vptr_basetype and
set_type_vptr_fieldno.  Remove the possibility for the type to be a
union in these functions.

Also, for the same reason, add an assertion that checks the type of
basetype in set_type_vptr_basetype.

I did not change the getters (internal_type_vptr_fieldno and
internal_type_vptr_basetype), because it seems like they are called by
code that handles similarly both structures and unions.  Making those
stricter would require adding conditions in those callers, which doesn't
look like an improvement.

Change allocate_cplus_struct_type to not use set_type_vptr_fieldno to
initialize the field to -1, otherwise it would trip the assertion when
initializing for a union type.

I stumbled on this while reviewing this change:

https://inbox.sourceware.org/gdb-patches/faa28230-4665-46f8-8d86-4c99262628d4@simark.ca/T/#t

Change-Id: Id9b2dc288f24d50eb50da46782b5ec6de5682e81
---
 gdb/gdbtypes.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index 75404d00e1ac..bd9abc7e7004 100644
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -1805,8 +1805,7 @@ void
 set_type_vptr_fieldno (struct type *type, int fieldno)
 {
   type = check_typedef (type);
-  gdb_assert (type->code () == TYPE_CODE_STRUCT
-	      || type->code () == TYPE_CODE_UNION);
+  gdb_assert (type->code () == TYPE_CODE_STRUCT);
   if (!HAVE_CPLUS_STRUCT (type))
     ALLOCATE_CPLUS_STRUCT_TYPE (type);
   TYPE_RAW_CPLUS_SPECIFIC (type)->vptr_fieldno = fieldno;
@@ -1831,8 +1830,8 @@ void
 set_type_vptr_basetype (struct type *type, struct type *basetype)
 {
   type = check_typedef (type);
-  gdb_assert (type->code () == TYPE_CODE_STRUCT
-	      || type->code () == TYPE_CODE_UNION);
+  gdb_assert (type->code () == TYPE_CODE_STRUCT);
+  gdb_assert (check_typedef (basetype)->code () == TYPE_CODE_STRUCT);
   if (!HAVE_CPLUS_STRUCT (type))
     ALLOCATE_CPLUS_STRUCT_TYPE (type);
   TYPE_RAW_CPLUS_SPECIFIC (type)->vptr_basetype = basetype;
@@ -3320,7 +3319,7 @@ allocate_cplus_struct_type (struct type *type)
   TYPE_RAW_CPLUS_SPECIFIC (type) = (struct cplus_struct_type *)
     TYPE_ZALLOC (type, sizeof (struct cplus_struct_type));
   *(TYPE_RAW_CPLUS_SPECIFIC (type)) = cplus_struct_default;
-  set_type_vptr_fieldno (type, -1);
+  TYPE_RAW_CPLUS_SPECIFIC (type)->vptr_fieldno = -1;
 }
 
 const struct gnat_aux_type gnat_aux_default =

base-commit: 329a53a6d590e2e90f590c89473990040a86c8e0
-- 
2.52.0