Re: libstdc++: ODR violation when using std::regex with and without -D_GLIBCXX_DEBUG

[Jonathan Wakely <jwakely dot gcc at gmail dot com>]

On 8 May 2018 at 14:00, Jonathan Wakely wrote:
> On 8 May 2018 at 13:44, Stephan Bergmann wrote:
>> I was recently bitten by the following issue (Linux, libstdc++ 8.0.1): A
>> process loads two dynamic libraries A and B both using std::regex, and A is
>> compiled without -D_GLIBCXX_DEBUG while B is compiled with -D_GLIBCXX_DEBUG.
>
> This is only supported in very restricted cases.
>
>> B creates an instance of std::regex, which internally creates a
>> std::shared_ptr<std::__detail::_NFA<std::__cxx11::regex_traits<char>>>,
>> where _NFA has various members of std::__debug::vector type (but which isn't
>> reflected in the mangled name of that _NFA instantiation itself).
>>
>> Now, when that instance of std::regex is destroyed again in library B, the
>> std::shared_ptr<std::__detail::_NFA<std::__cxx11::regex_traits<char>>>::~shared_ptr
>> destructor (and functions it in turn calls) that happens to get picked is
>> the (inlined, and exported due to default visibility) instance from library
>> A.  And that assumes that that _NFA instantiation has members of non-debug
>> std::vector type, which causes a crash.
>>
>> Should it be considered a bug that such mixture of debug and non-debug
>> std::regex usage causes ODR violations?
>
> Yes, but my frank response is "don't do that".
>
> The right fix here might be to ensure that _NFA always uses the
> non-debug vector even in Debug Mode, but I'm fairly certain there are
> other similar problems lurking.

N.B. I think this discussion belongs on the libstdc++ list.