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From: "vultkayn at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug analyzer/109365] Double delete yields -Wanalyzer-use-after-free
 instead of -Wanalyzer-double-free
Date: Fri, 07 Jul 2023 11:28:44 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109365

Benjamin Priour <vultkayn at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|dmalcolm at gcc dot gnu.org        |vultkayn at gcc dot=
 gnu.org

--- Comment #4 from Benjamin Priour <vultkayn at gcc dot gnu.org> ---
(In reply to Benjamin Priour from comment #3)
[...snip...]
>=20
>=20
>   <bb 3> :
>   *a.0_11 =3D{v} {CLOBBER};
>   operator delete (a.0_11, 8);
>
[...snip...]=20
>
> Entry statement of bb3 is the one actually detected as
> -Wanalyzer-double-free.

Given the above IPA, we cannot just ignore the assignment statement, as it
could really be an injurious statement, not just a pre-deallocation stateme=
nt
at it is now.

Consider the code:
  A* a;
  ...
  delete a;
  a->x =3D 7; // (1)
  operator delete (a); (2)=20=20

On my box, (1) and (2) generated the IPA
<bb 4> :
  a_10->a =3D 7;
  operator delete (a_10);

Thus, I'd first only consider types where a destructor is provided (by the =
user
or generated).
Indeed, when a destructor is supplied for a type, <bb 3> becomes something =
akin
to :

struct A
{
  ...
  ~A() {}
}

...

<bb 3> :
  A::~A (a.0_12);
  operator delete (a.0_12, 8);


The warnings stay the same, though it is now more reliable to check for a
destructor call, instead any random single assignment. I'm considering addi=
ng a
new state to sm-malloc, RS_DESTROYED, that would also help flag use after
standalone destruction (without a succeeding deallocation).=