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

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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.
This commit is contained in:
Jakub Jelinek 2020-04-08 15:30:16 +02:00
parent a6479aa4c0
commit 4cf6b06cb5
4 changed files with 40 additions and 7 deletions
gcc
cp
ChangeLogdecl.c
testsuite
ChangeLog
g++.dg/ubsan
vptr-15.C

8
gcc/cp/ChangeLog

@ -1,3 +1,11 @@
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.
2020-04-08 Marek Polacek <polacek@redhat.com>
PR c++/94478 - ICE with defaulted comparison operator

20
gcc/cp/decl.c

@ -16663,14 +16663,20 @@ begin_destructor_body (void)
/* If the vptr is shared with some virtual nearly empty base,
don't clear it if not in charge, the dtor of the virtual
nearly empty base will do that later. */
if (CLASSTYPE_VBASECLASSES (current_class_type)
&& CLASSTYPE_PRIMARY_BINFO (current_class_type)
&& BINFO_VIRTUAL_P
(CLASSTYPE_PRIMARY_BINFO (current_class_type)))
if (CLASSTYPE_VBASECLASSES (current_class_type))
{
stmt = convert_to_void (stmt, ICV_STATEMENT,
tf_warning_or_error);
stmt = build_if_in_charge (stmt);
tree c = current_class_type;
while (CLASSTYPE_PRIMARY_BINFO (c))
{
if (BINFO_VIRTUAL_P (CLASSTYPE_PRIMARY_BINFO (c)))
{
stmt = convert_to_void (stmt, ICV_STATEMENT,
tf_warning_or_error);
stmt = build_if_in_charge (stmt);
break;
}
c = BINFO_TYPE (CLASSTYPE_PRIMARY_BINFO (c));
}
}
finish_decl_cleanup (NULL_TREE, stmt);
}

5
gcc/testsuite/ChangeLog

@ -1,3 +1,8 @@
2020-04-08 Jakub Jelinek <jakub@redhat.com>
PR c++/94325
* g++.dg/ubsan/vptr-15.C: New test.
2020-04-08 Marek Polacek <polacek@redhat.com>
PR c++/94478 - ICE with defaulted comparison operator

14
gcc/testsuite/g++.dg/ubsan/vptr-15.C Normal file

@ -0,0 +1,14 @@
// PR c++/94325
// { dg-do run { target c++11 } }
// { dg-options "-fsanitize=vptr -fno-sanitize-recover=vptr" }
struct A { virtual ~A () = default; };
struct B : public virtual A {};
struct C : public B {};
struct D : public C {};
int
main ()
{
D a;
}