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From: "sbergman at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/100797] New: using declaration causing virtual call with
 wrongly adjusted this pointer
Date: Thu, 27 May 2021 10:37:15 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100797

            Bug ID: 100797
           Summary: using declaration causing virtual call with wrongly
                    adjusted this pointer
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sbergman at redhat dot com
  Target Milestone: ---

(I stripped this down from an issue found in LibreOffice,
<https://git.libreoffice.org/core/+/0d3dd9d9f6f0e6236c8db8ebdea44c78854639a=
8%5E%21>
"tdf#142467 crash on calling 'getInfoHelper' in final class", where the
original code had the most derived class, S4 in the below stripped down
example, marked as final, and where removing the "final" fixed things.  In =
the
below stripped down example, there is no difference in behavior whether or =
not
S4 is marked final, but I hope the issue exposed by the stripped down examp=
le
is still the same as the one originally experienced in the LibreOffice code=
.)

At least with gcc-11.1.1-1.fc34.x86_64 and with a recent trunk build towards
GCC 12:

> $ cat test.cc
> #include <iostream>
> struct S1 { virtual ~S1() =3D default; };
> struct S2 { virtual void f1() =3D 0; };
> struct S3: S1, S2 {
>     void f1() { f2(); }
>     virtual void f2() =3D 0;
> };
> struct S4: S3 {
>     void f2() { std::cout << "called\n"; }
>     using S2::f1;
> };
> int main() { S4().f1(); }

> $ g++ test.cc
> $ ./a.out
> Segmentation fault

instead of printing "called".  The issue goes away when removing the

  using S2::f1;

declaration from S4.=