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From: "vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug gdb/31281] [gdb] intrusive_list.h:329: internal-error:
 push_back: Assertion elem_node->prev == INTRUSIVE_LIST_UNLINKED_VALUE failed.
Date: Wed, 24 Jan 2024 19:41:18 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D31281

--- Comment #8 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Simon Marchi from comment #6)
> I bisected gcc, the failure appeared with this commit:
>=20
> c++: non-dependent .* operand folding [PR112427]
> https://gitlab.com/gnutools/gcc/-/commit/d3f48f68227
>=20
> I know nothing about compilers, so I don't know what the code changes.  B=
ut
> the included test case uses a pointer-to-member, which is somewhat releva=
nt
> in our case.

At the parser level (original tree dump file), I see:
...
;; Function static intrusive_list_node<T>* intrusive_member_node<T,
MemberNode>::as_node(T*) [with T =3D thread_info; intrusive_list_node<T> T:=
:*
MemberNode =3D &thread_info::resumed_with_pending_wait_status_node] (null)
;; enabled by -tree-original


return <retval> =3D NON_LVALUE_EXPR <elem> !=3D 0B ? &NON_LVALUE_EXPR
<elem>->D.191606 + (sizetype) 520 : (struct intrusive_list_node *) 520;
...

The 520 is the offset of resumed_with_pending_wait_status_node:
...
(gdb) p /x (void *)&thread->resumed_with_pending_wait_status_node - (void
*)thread
$46 =3D 0x208
(gdb) p 0x208
$12 =3D 520
...

The D.191606 bit adds an offset of 8 (this becomes apparent at the expand r=
tl
dump file).  That also happens to be the offset of the inherited intrusive =
list
node, see:
...
class thread_info : public refcounted_object,
                    public intrusive_list_node<thread_info>
...
and:
...
(gdb) p (void *) &thread.next - (void *) thread
$13 =3D 8
...

--=20
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