<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/64807>64807</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Is it expected that --relocatable-pch accepts relative isysroot and tries to match source paths against it?
        </td>
    </tr>

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

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

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

<pre>
    As title asks. I am not sure if it is expected or not. I stumbled into it while trying to use ccache with base_dir when creating relocatable header - ccache changed `isysroot` argument from absolute path to `.`, then Clang promptly failed to match any sources against it.

As I saw in produced PCH files, source paths are not canonized, they may contain `..` parts for example. From this I take that `isysroot` should not be canonized as well but I'm not sure.

Reproducer can be found here https://github.com/ccache/ccache/issues/1322
</pre>
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