<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/62424>62424</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            cmake fails to generate correct build.ninja with LLVM under chroot
        </td>
    </tr>

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

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

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

<pre>
    I have cmake-3.26.3-1.1.x86_64. With this minimal `CMakeLists.txt`:
```cmake
cmake_minimum_required(VERSION 3.3.0)

project(pokus VERSION 1.0.0 LANGUAGES C CXX)

find_package(LLVM REQUIRED CONFIG)

include(AddLLVM)
```
I see this error at the end of `mkdir b; cd b; cmake .. -GNinja` when done in a chroot environment:
```
...
-- Generating done (0.0s)
CMake Error:
 Running

   '/bin/ninja' '-C' '/home/jslaby/pokus/b' '-t' 'recompact'

  failed with:

   ninja: error: build.ninja:114: multiple rules generate /lib64/cmake/llvm/LLVM-Config.cmake
```
It is likely because `build.ninja` `build` target contains both of these:
```
//lib64/cmake/llvm/LLVM-Config.cmake
/lib64/cmake/llvm/LLVM-Config.cmake
```
In normal root, `build.ninja` contains instead: `/usr/lib64/cmake/llvm/LLVM-Config.cmake`. And that one exists also in the chroot as `/lib64` is linked to `/usr/lib64` in both environments.

`/usr/lib64/cmake/llvm/LLVMConfig.cmake` does this:
```cmake
get_filename_component(LLVM_INSTALL_PREFIX "${CMAKE_CURRENT_LIST_FILE}" PATH)
get_filename_component(LLVM_INSTALL_PREFIX "${LLVM_INSTALL_PREFIX}" PATH)
get_filename_component(LLVM_INSTALL_PREFIX "${LLVM_INSTALL_PREFIX}" PATH)
get_filename_component(LLVM_INSTALL_PREFIX "${LLVM_INSTALL_PREFIX}" PATH)
```
Which returns `/usr` in normal root. And `/` in chroot. For some reason, in chroot, `cmake` tries to open `/usr/lib64/cmake/llvm/LLVMConfig.cmake` first, but in chroot `/lib64/cmake/llvm/LLVMConfig.cmake` is tried first (according to `strace`). They are the same files (see above), but `cmake` doesn't try them with the same order.

So those `get_filename_component()` of `LLVMConfig.cmake` look broken in this respect -- they should set an empty string to `LLVM_INSTALL_PREFIX` and not `/`?
</pre>
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