One of my packges gives a message with the undefined behaviour sanitiser
(UBSAN). I have difficulty tracking down/understanding the cause of this
message. However, I have been able to create a small example that
generates the same warning. The mail below is a bit on the long side,
and, I hope it is readable as it mixes quite a lot code with text. I am
sorry for that. A probably better readable version can be found at
https://github.com/djvanderlaan/lvec_ubsan where also the complete
source code and the docker image used for testing can be found.
My example consists of two packages: pkg1 and pkg2. The package pkg2
links to pkg1. Package pkg1 defines a template class `FooBar<T>` which
inherits from virtual class `Foo`. Pointers to the these objects are
passed back to R using a `Rcpp:XPtr` object:
========== pkg1/src/construct.cpp ================
#include "../inst/include/pkg1.h"
// [[Rcpp::export]]
RcppExport SEXP new_foobar(int i) {
BEGIN_RCPP
FooBar<int>* x = new FooBar<int>(i);
return Rcpp::XPtr<Foo>(x, true);
END_RCPP
}
// [[Rcpp::export]]
RcppExport SEXP new_foobard(double i) {
BEGIN_RCPP
FooBar<double>* x = new FooBar<double>(i);
return Rcpp::XPtr<Foo>(x, true);
END_RCPP
}
========== END pkg1/src/construct.cpp ================
All headers of pkg1 are `inst/include`; these are included by `pkg2`:
========== pkg1/inst/include/pkg1.h ================
#include <Rcpp.h>
// ==== VISITOR
template<typename T> class FooBar;
class FooBarVisitor {
public:
virtual void visit(FooBar<double>& vec) = 0;
virtual void visit(FooBar<int>& vec) = 0;
};
// ==== FOO
class Foo {
public:
Foo() {};
virtual ~Foo() {};
virtual void visit(FooBarVisitor* visitor) = 0;
};
// ==== FOOBAR
template<typename T>
class FooBar : public Foo {
public:
FooBar(T i = 0) : Foo(), i_(i) {};
~FooBar() {};
T i() const { return i_;}
void i(T i) { i_ = i;}
void visit(FooBarVisitor* visitor) {
visitor->visit(*this);
}
private:
T i_;
};
#endif
========== END pkg1/inst/include/pkg1.h ================
The XPtr is passed to c++ code in pkg2 and methods of the Foo object are
called:
========== pkg2/src/construct.cpp ================
#include <Rcpp.h>
#include <pkg1.h>
// [[Rcpp::export]]
RcppExport int get_foobar(SEXP xp) {
Rcpp::XPtr<Foo> x(xp);
Foo* y1 = x;
FooBar<int>* y2 = dynamic_cast<FooBar<int>*>(y1);
return y2->i();
}
========== END pkg2/src/construct.cpp ================
This generates the following UBSAN messages:
========== WARNING MESSAGES ================
Testing pkg2
<U+221A> | OK F W S | Context
/ | 0 | fooconstruct.cpp:9:21: runtime error: <null> address
0x000003c21810 which does not point to an object of type 'Foo'
0x000003c21810: note: object is of type 'FooBar<int>'
00 00 00 00 58 1c 79 fd 48 7f 00 00 0a 00 00 00 00 00 00 00 20
00 00 00 00 00 00 00 01 03 00 00
^~~~~~~~~~~~~~~~~~~~~~~
vptr for 'FooBar<int>'
construct.cpp:10:14: runtime error: member call on address
0x000003c21810 which does not point to an object of type 'FooBar<int>'
0x000003c21810: note: object is of type 'FooBar<int>'
00 00 00 00 58 1c 79 fd 48 7f 00 00 0a 00 00 00 00 00 00 00 20
00 00 00 00 00 00 00 01 03 00 00
^~~~~~~~~~~~~~~~~~~~~~~
vptr for 'FooBar<int>'
/usr/local/lib/R/library/pkg1/include/pkg1.h:33:26: runtime error:
member access within address 0x000003c21810 which does not point to an
object of type 'const FooBar<int>'
0x000003c21810: note: object is of type 'FooBar<int>'
00 00 00 00 58 1c 79 fd 48 7f 00 00 0a 00 00 00 00 00 00 00 20
00 00 00 00 00 00 00 01 03 00 00
^~~~~~~~~~~~~~~~~~~~~~~
vptr for 'FooBar<int>'
<U+221A> | 1 | foo
========== END WARNING MESSAGES ================
I have had real problem reproducing this error. Also searching for the
error give little clues as to what the problem is. The following message
on the Rcpp-devel list seems somewhat similar:
http://lists.r-forge.r-project.org/pipermail/rcpp-devel/2017-July/009656.html.
I thought that it might be caused by the fact that I am passing pointers
to template classes between libraries. I also couldn't find much about
that. I did find some messages on passing pointers to STL objects
between libraries. That should be ok, as long as the same compiler is
used for both libraries. Although that might technically still make it
undefined behaviour.
So, help!?
Jan
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