Hi!
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.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Or do we want some other test?
2020-04-06 Jakub Jelinek <ja...@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.
--- gcc/cp/decl.c.jj 2020-03-27 09:59:26.407083563 +0100
+++ gcc/cp/decl.c 2020-04-06 13:25:03.321511554 +0200
@@ -16662,14 +16662,20 @@ 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);
}
--- gcc/testsuite/g++.dg/ubsan/vptr-15.C.jj 2020-04-06 13:32:43.501627756
+0200
+++ gcc/testsuite/g++.dg/ubsan/vptr-15.C 2020-04-06 13:37:52.642001353
+0200
@@ -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;
+}
Jakub
