Clang Memory sanitizer triggers error in string -> float conversion

[jzmaddock]

I haven't been able to figure out if this is a real issue or not, but it is super-annoying as it prevents running the multiprecision tests with -fsanitize=memory.

If I compile:

#include <boost/lexical_cast.hpp>

int main()
{
   std::string s("3.14");
   float f = boost::lexical_cast<float>(s);
}

With clang++ -fsanitize=memory then I see:

==11560==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x49b367 in bool boost::detail::lexical_ostream_limited_src<char, std::char_traits<char> >::shr_using_base_class<float>(float&) /home/jzm/boost/libs/multiprecision/test/../../../boost/lexical_cast/detail/converter_lexical_streams.hpp:594:17
    #1 0x49a4bc in bool boost::detail::lexical_ostream_limited_src<char, std::char_traits<char> >::float_types_converter_internal<float>(float&) /home/jzm/boost/libs/multiprecision/test/../../../boost/lexical_cast/detail/converter_lexical_streams.hpp:744:43
    #2 0x499eb1 in boost::detail::lexical_ostream_limited_src<char, std::char_traits<char> >::operator>>(float&) /home/jzm/boost/libs/multiprecision/test/../../../boost/lexical_cast/detail/converter_lexical_streams.hpp:769:53
    #3 0x499219 in boost::detail::lexical_converter_impl<float, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >::try_convert(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, float&) /home/jzm/boost/libs/multiprecision/test/../../../boost/lexical_cast/detail/converter_lexical.hpp:485:26
    #4 0x498e39 in bool boost::conversion::detail::try_lexical_convert<float, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, float&) /home/jzm/boost/libs/multiprecision/test/../../../boost/lexical_cast/try_lexical_convert.hpp:201:20
    #5 0x498c35 in float boost::lexical_cast<float, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) /home/jzm/boost/libs/multiprecision/test/../../../boost/lexical_cast.hpp:41:14
    #6 0x4989ea in main /home/jzm/t.cpp:6:14
    #7 0x7fa75f7d11e2 in __libc_start_main /build/glibc-5mDdLG/glibc-2.30/csu/../csu/libc-start.c:308:16
    #8 0x41d4bd in _start (/home/jzm/boost/libs/multiprecision/test/a.out+0x41d4bd)

SUMMARY: MemorySanitizer: use-of-uninitialized-value /home/jzm/boost/libs/multiprecision/test/../../../boost/lexical_cast/detail/converter_lexical_streams.hpp:594:17 in bool boost::detail::lexical_ostream_limited_src<char, std::char_traits<char> >::shr_using_base_class<float>(float&)

[pdimov]

Line boost/lexical_cast/detail/converter_lexical_streams.hpp:594:17 is

                stream.exceptions(std::ios::badbit);

where stream has just been declared as

                std::basic_istream<CharT, Traits> stream(&buf);

so this doesn't look like a legitimate lexical_cast issue. The documentation of -fsanitize=memory says that all code needs to be instrumented, and in this case the standard library probably hasn't been.

[apolukhin]

@pdimov is absolutely right - msan requires instrumentation for all the code, including C++ Standard Library, libc and c++ runtimes.

We use lexical_cast in some projects that build and test the whole world with msan, no issues so far