https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103086
Bug ID: 103086
Summary: [11/12 Regression] std::unique_ptr printer gets
confused by [[no_unique_address]] in tuple
Product: gcc
Version: 11.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
When using GDB 11 or 12 and GCC 11 or 12 the pretty printer for std::unique_ptr
shows the value of the deleter instead of the pointer:
$1 = std::unique_ptr<datum> = {get() = {<No data fields>}}
I filed this as https://sourceware.org/bugzilla/show_bug.cgi?id=28480 but with
Bruno's help we realised it's actually a libstdc++ printer bug.
The problem is that since std::tuple started using [[no_unique_address]] the
tuple<T*, default_delete<T>> object has two _M_head_impl subobjects, in
different base classes. That means this printer code is ambiguous:
tuple_head_type = tuple_impl_type.fields()[1].type # _Head_base
head_field = tuple_head_type.fields()[0]
if head_field.name == '_M_head_impl':
self.pointer = tuple_member['_M_head_impl']
In older versions of GDB it happened to work by chance, because GDB returned
the last _M_head_impl member and std::tuple's base classes are stored in
reverse order, so the last one was the T* element of the tuple. Since GDB 11 it
returns the first _M_head_impl, which is probably more sensible, but now the
printer gets the default_delete<T> element.
The fix is for the printer to stop using an ambiguous field name and cast the
tuple to the right base class before accessing the _M_head_impl member:
--- a/libstdc++-v3/python/libstdcxx/v6/printers.py
+++ b/libstdc++-v3/python/libstdcxx/v6/printers.py
@@ -258,7 +258,7 @@ class UniquePointerPrinter:
tuple_head_type = tuple_impl_type.fields()[1].type # _Head_base
head_field = tuple_head_type.fields()[0]
if head_field.name == '_M_head_impl':
- self.pointer = tuple_member['_M_head_impl']
+ self.pointer = tuple_member.cast(tuple_head_type)['_M_head_impl']
elif head_field.is_base_class:
self.pointer = tuple_member.cast(head_field.type)
else:
