<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/59536>59536</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            ld.ldd: error: undefined symbol but the symbol exists?
        </td>
    </tr>

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

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

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

<pre>
    Hi!

We are bumping our compiler from 1ae33bf42680b156fe0f5cd6163bf24ef45d8cd3 to 61311f3c9363534eda3bc9b8a5edbab80048cdd4 and now we get the following linker error in our code:

```
ld.lld: error: undefined symbol: Eigen::Matrix<double, 2, 1, 0, 2, 1>::Matrix()
>>> referenced by foo.cpp
>>>               foo.pic.o
>>> did you mean: Eigen::Matrix<double, 2, 1, 0, 2, 1>::Matrix()
>>> defined in: bar.a
```

I'm not sure what the error message is trying to tell me - the symbol is clearly available, what exactly is the problem? I don't know what action I should take as a user to fix this.

To clarify, `foo.cpp` includes `<Eigen/Core>` which should provide the definition for `Eigen::Matrix` so I can't really tell what the problem is.
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJy0VMuOrDYQ_RqzKQ3yA-hmwWIy96LMIrtIWftRgDMGI9tMD_n6yNCT9J1E2aVlVWO7HqfOsS1jtOOC2JH6J1J_K-SWJh86LYPzcZTuHf9YC-XN3v1sCWeEfiP0-bS_IciAoLZ5tcsIfgug_bxahwGG4GdgEoVQQ8WbK1WsbgakQ61NwxqhBl7hUNXmqo2A5KFhgrFB6FY0ohYVGimUbtVV1miUVFdKq6s2pgK5GFj8DW4IIyZIE8LgnfO3jMHZ5Q0DYAg-gF3umAwS8fyInDT0Po6pM6VzhojnMzB_bIvBwS5oIO6z8i6vfbcjLjmTeP5FpmA_iHgxflMOCX8Bng3Lhj5MxfcfAviV8PaOIW_lAQEHDLhoNKB2GLwv9bp-dfrxl51Wq0v_1c1YA7vfYEa5_J-YP9mxRxUlQyn_ldrTvhJ-mWHxCeIWEG6TPIU7dZoxRjki2Agp7FnG5CGhczAjPB2OpwjZQzuUwe0g36V18t7HkRA_pE5uP9JMCGvwyuFMRA-vYPxC-CXB23FysrfUyfoFXiFOfnMGknxDkBEkbBFDRjDYD0iTjeVjJ7960E4GO-y5Lmnop1wNBbtotxmMeZmIl5N63r_4gJm1hsJtsnr6rLgG_24NHmAPOu2BaPAhJ_incA2F6OEVtDx7CSid20-i_mL03jXYWBamE6YVrSywY82FMVa1rC2mTrOLYo0RqOmFYWOQXsSlrrhgFbIrqwrbcco546xmlahZW0pdN7yljF0GKq50IBXFWVpXOvc-lz6MhY1xw65ua9EUTip08XhQOF_wBscm4Ty_L6HLMU9qGyOpqLMxxb-zJJscdvk6mv--jqC29Hgw8CMnIqIvtuC6KaU1Zu54T3g_2jRtqtR-JrzPpe5_T2vwv6NOhPcHwEh4fzTwZwAAAP__09KOaA">