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Re: How to ensure C++ classes don't go missing with -flto?


On Fri, 25 Jan 2019 at 01:34, Jeffrey Walton <noloader@gmail.com> wrote:
>
> This question on Stack Overflow caught my eye:
> https://stackoverflow.com/q/54345531/608639 . In the question a
> program compiles and links fine without -flto. With -flto symbols go
> missing.
>
> One of the classes that go missing is RSAFunction, which performs
> exponentiation with a public key. The source code is available at
> https://github.com/weidai11/cryptopp/blob/master/rsa.h and
> https://github.com/weidai11/cryptopp/blob/master/rsa.cpp.
>
> There does not seem to be anything special about rsa.h and rsa.cpp
> from my view of the issue. The header declares the classes, and then
> the source file implements the classes.
>
> How does one ensure a class does not go missing when using -flto?

You don't do anything. Classes don't "go missing" unless there's a bug
somewhere.

The symptoms look like libcryptopp was compiled with -fno-rtti, but
maybe there's a GCC bug.

There's no way to analyse it further (there's no mention of which
version of GCC is used and how libcryptopp was compiled).

>
> (Is this like implicit template instantiations? Is there a way to
> declare it so that it does not go missing?)


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