<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/61571>61571</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            ASan runtime has unsatisfiable undefined references to __extend* builtins on Android
        </td>
    </tr>

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

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

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

<pre>
    Because the ASan runtime is linked with `-nodefaultlibs` per the various things that add the flag in different `CMakeFiles.txt` under `compiler-rt/`, when compiling compiler-rt for Android with clang, references to `__extend*` builtins from calls added by the compiler in `__ubsan::Value::getFloatValue()` are left undefined (since libclang_rt.builtins is not linked in), and later on, that can yield linker errors when linking against that ASan runtime, because the linker (BFD) sees the visibility-hidden `__extend*` symbols from libclang_rt.builtins and doesn't like that it's the only thing that resolves the ASan runtime symbols (hidden symbol `__extenddftf2' in linux/libclang_rt.builtins-x86_64-android.a(extenddftf2.c.o) is referenced by DSO). Or even later on, that can yield dynamic loader errors when loading the ASan runtime requires those symbols that can't be found anywhere.

As a matter of fact, building compiler-rt via `runtimes` with `-DLLVM_ENABLE_RUNTIMES=compiler-rt` fails to build entirely because it adds `-Wl,-z,defs`, which barfs about the undefined symbols directly (which, BTW, include libunwind symbols too).
</pre>
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