<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/139440>139440</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            -fwhole-program-vtables breaks in combination with -ffat-lto-objects
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          Jannik2099
      </td>
    </tr>
</table>

<pre>
    the following

```cpp
#include <stdexcept>

struct Foo : std::runtime_error {
    Foo() : runtime_error("") {}
};

Foo foo{};
```

when built into an object file with
`clang++ -flto=thin -fwhole-program-vtables -ffat-lto-objects -fPIC -fvisibility=hidden -c foo.cpp -o foo.o`
and then linked into a shared library with
`clang++ -flto=thin -shared foo.o -o foo.so`
will fail with
`ld.lld: error: undefined hidden symbol: vtable for Foo`

Removing either the `-fwhole-program-vtables` or `-ffat-lto-objects` when compiling the object file works fine.

Note that this isn't related to this specific underlying type, I only discovered it with `std::runtime_error` first. Reproduces on libstdc++ and libc++ (when linking dynamically)
</pre>
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