<html>
    <head>
      <base href="https://llvm.org/bugs/" />
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW --- - "--sysroot /" mess up overlaid VFS"
   href="https://llvm.org/bugs/show_bug.cgi?id=27909">27909</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>"--sysroot /" mess up overlaid VFS
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>clang
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>unspecified
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>PC
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>Linux
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>Frontend
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedclangbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>fs.output@gmail.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvm-bugs@lists.llvm.org
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr></table>
      <p>
        <div>
        <pre>Virtual file system cannot find overlaid file if "--sysroot /" is specified.

Way to reproduce:
$ cat overlay.yml
{
    "version": 0,
    "use-external-names": false,
    "roots": [
        {
            "type": "file",
            "name": "/usr/include/stdio_vfs.h",
            "external-contents": "/usr/include/stdio.h"
        }
    ]
}
$ cat foo.c
#include <stdio_vfs.h>
int main() {
    printf("foo");
}
$ clang -ivfsoverlay overlay.yml foo.c  # NO PROBLEM
$ clang --sysroot / -ivfsoverlay overlay.yml foo.c
foo.c:1:10: fatal error: 'stdio_vfs.h' file not found
#include <stdio_vfs.h>
         ^
1 error generated.
$</pre>
        </div>
      </p>
      <hr>
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    </body>
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