<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/120003>120003</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            LLVM build is completely broken is LLVM_USE_SANITIZER is set to "Undefined" and g++ is the host compiler
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            build-problem
      </td>
    </tr>

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

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

<pre>
    The documentation says nothing about restrictions of LLVM_USE_SANITIZER variables (e.g the host compiler has to be clang)
"**LLVM_USE_SANITIZER**:STRING
 Define the sanitizer used to build LLVM binaries and tests. Possible values
 are ``Address``, ``Memory``, ``MemoryWithOrigins``, ``Undefined``, ``Thread``,
  ``DataFlow``, and ``Address;Undefined``. Defaults to empty string."

I attach the file with all errors that i got during configure and compilation stages

[llvm_errs_sanitizer_undefined_gcc.log](https://github.com/user-attachments/files/18140824/llvm_errs_sanitizer_undefined_gcc.log)


cmake command i use:
```
cmake -G "Unix Makefiles"                      \
 -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_INSTALL_PREFIX=/usr \
 -DLLVM_BINUTILS_INCDIR=/usr/include \
 -DLLVM_HOST_TRIPLE="x86_64-unknown-linux-gnu" \
 -DLLVM_USE_SANITIZER="Undefined" \
    -DLLVM_BUILD_LLVM_DYLIB=ON \
 -DLLVM_LINK_LLVM_DYLIB=ON \
    -DLLVM_INSTALL_UTILS=ON \
 -DLLVM_ENABLE_RTTI=ON \
    -DLLVM_ENABLE_FFI=ON \
 -DLLVM_ENABLE_PROJECTS="clang;compiler-rt;lld;bolt" \
 -DCLANG_LINK_CLANG_DYLIB=ON \
    -DLLDB_USE_SYSTEM_SIX=1 \
 -DLIBOMP_INSTALL_ALIASES=OFF \
    -DLLVM_TARGETS_TO_BUILD="X86;ARM" \
 -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" \
 -DPOLLY_ENABLE_GPGPU_CODEGEN=ON \
    ../llvm
```
</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJyMVd1uqzgXfRrnxkoEhqTJRS6gQD6-Q36UkJnTuUEGdsBTx1S26c88_cgmbU_T9mgiJByz9_Jay_beVCnWCIAlmoZoGo1or9tOLqsWlBYv9-2o7OqXZd4CrruqP4PQVLNOYEVfFBadbploMC27XmMJSktWmc8KdyecZX-si-MhLg7BJs3Tv-I9fqSS0ZKDwojMYdJg3QJuO6Vx1Z0fGAeJW6qw7nAJuOJUNIgskBMgQhAJEAk-Yw7zyAsO-T7drJAT4AhOTIDFVlQwzf4BiXsFtQXuGa8tN1wyQSUDhamosQal1QTvOqVYyQE_Ut6DMnBUAkYzB82coK4lKDX8QeT2Mr2Gcydfvp79k-l2K1nDxKe0o6gt0fr6Q95KoO-zhsPlS0Q1TXj39J5hqH8k54VXwBNjCO25tsbC-UG_YLNTopkYX50AOUGKqda0aq1pJ8YBPzHdYso5Bik7qbBuqcYMN53GdW-ScdWJE2t6CZbEsIGXw6FpY70zzzTk_PFcgJSqeNuOon_lWDRVNeFdg6YRIvNW6weFvACRBJGkYbrty0nVnRFJegVyPLA0x1Ahkhii5u3OXd-ZEx-R5L-tNRwq-1Rneg-G_dmoYOacmPWd4OLxzHkLGq8wIuQo2DNe03u4rE7wlz80tRs3jm7XwY-4CI9pFhX53S5GXrQHDlTBawzGb2Hp5pAHWVbs9nGS_kReZIXLdzR7AcJ0c8zT7FCkm9so3b-FIZIwUfG-hquE_20PeZHv010W22DyPJ8VM3_ci3vRPYkxZ6J_HjeiN3I-pn68bDb5_Xy9R1sNAzmr1A6juywNkRdtN1egWbr58V3IO9KrGVbrVzDxJgizuNjnefoNxCUiSdLf5O_22__Ht_lhUDeUHS98rUhjqZEXcl4jLyw7rj9YdJsFm9UgZxh-qycKByvvDnm8Lg52c91f-KThdr17kxxkaXCIregk-SwrD_arOD8U-Xawe2D-cz5DXhjs15938dWp4yZP1_FFKWdl9fxsxNkBLdkw7sUTE_UHkN02y-5eUVa71e5Y3G6jeBVvrrVOJpdb-OsVGtVLr154CzqCpXvj-eTGJwt_1C792dxdOO7M8z33hlZQO3RGvUV9uqHeYn7yR2xJHOK7xJ26_tT1_Ak4lQOkXpT1yaU-zJDvwJkyPjFrTjrZjJhSPSxd4jiON-K0BK5sdyPE1v7xg-xKDmdT-6bRSC5N4rjsG4V8hzPTBd6gNNMclkOzsH2DKVvoOGjgL7iU3T0IM_lFr2MKK9Cm5F5fGVNoGkRCREIT9akHjnrJl7-phNbd4WXE_A2VNjffyLbVcFD-uCT_BgAA__8IRVtl">