[Bug sanitizer/94325] [8/9 Regression] UBSAN: "invalid vptr" false positive for virtual inheritance with -fno-sanitize-recover=all

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94325

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-9 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:175f052446556d32e887e1658a5a92c3c2f3a6f5

commit r9-8875-g175f052446556d32e887e1658a5a92c3c2f3a6f5
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Apr 8 15:30:16 2020 +0200

    c++: Further fix for -fsanitize=vptr [PR94325]

    For -fsanitize=vptr, we insert a NULL store into the vptr instead of just
    adding a CLOBBER of this.  build_clobber_this makes the CLOBBER conditional
    on in_charge (implicit) parameter whenever CLASSTYPE_VBASECLASSES, but when
    adding this conditionalization to the -fsanitize=vptr code in PR87095,
    I wanted it to catch some more cases when the class has
CLASSTYPE_VBASECLASSES,
    but the vptr is still not shared with something else, otherwise the
    sanitization would be less effective.
    The following testcase shows that the chosen test that
CLASSTYPE_PRIMARY_BINFO
    is non-NULL and has BINFO_VIRTUAL_P set wasn't sufficient,
    the D class has still sizeof(D) == sizeof(void*) and thus contains just
    a single vptr, but while in B::~B() this results in the vptr not being
    cleared, in C::~C() this condition isn't true, as CLASSTYPE_PRIMARY_BINFO
    in that case is B and is not BINFO_VIRTUAL_P, so it clears the vptr, but
the
    D::~D() dtor after invoking C::~C() invokes A::~A() with an already cleared
    vptr, which is then reported.
    The following patch is just a shot in the dark, keep looking through
    CLASSTYPE_PRIMARY_BINFO until we find BINFO_VIRTUAL_P, but it works on the
    existing testcase as well as this new one.

    2020-04-08  Jakub Jelinek  <jakub@redhat.com>

            PR c++/94325
            * decl.c (begin_destructor_body): For CLASSTYPE_VBASECLASSES class
            dtors, if CLASSTYPE_PRIMARY_BINFO is non-NULL, but not
BINFO_VIRTUAL_P,
            look at CLASSTYPE_PRIMARY_BINFO of its BINFO_TYPE if it is not
            BINFO_VIRTUAL_P, and so on.

            * g++.dg/ubsan/vptr-15.C: New test.

    (cherry picked from commit 4cf6b06cb5b02c053738e2975e3b7a4b3c577401)