Suppress UndefinedBehaviorSanitizer warnings from external libraries

Question

I have an UndefinedBehaviorSanitizer build (-fsanitize=undefined), and I am trying to suppress a warning for UB in an external library that is out of my control. The clang/gcc docs mention __attribute__((no_sanitize("undefined"))), but to my surprise it seems that this attribute does not suppress warnings from subroutines.

Simple example:

//__attribute__((no_sanitize("shift"))) // this correctly suppresses the warning
int bar() {
    return 1 << 64;
}

__attribute__((no_sanitize("shift"))) // this does not
int foo() {
    return bar();
}

int main() {
    foo();
    return 0;
}

Since this attribute doesn't seem to work, how can I suppress this warning? I could remove the entire target from my UBSan build, but that seems incredibly heavy-handed.

Answer 1

Clang has pragmas to apply attributes in bulk:

#pragma clang attribute push (__attribute__((no_sanitize("undefined"))), apply_to=function)
// ...
#pragma clang attribute pop

Wrapping the header in those disables the check in your example:

#pragma clang attribute push (__attribute__((no_sanitize("undefined"))), apply_to=function)
#include <boost/ptr_container/ptr_vector.hpp>
#pragma clang attribute pop

struct Foo{};

void bar()
{
    boost::ptr_vector<boost::nullable<Foo>> v;
    v.push_back(nullptr);
    v.push_back(new Foo);
}

int main()
{
    bar();
}