<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Issue</th>
<td>
<a href=https://github.com/llvm/llvm-project/issues/127764>127764</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>
Building runtimes fails for LLVM 20.1.0-rc2
</td>
</tr>
<tr>
<th>Labels</th>
<td>
new issue
</td>
</tr>
<tr>
<th>Assignees</th>
<td>
</td>
</tr>
<tr>
<th>Reporter</th>
<td>
BalderOdinson
</td>
</tr>
</table>
<pre>
**Setup**
OS: Ubuntu 18.04 x86_64
Compiler: Clang: 19.1.7
Tool versions:
- CMake 3.20.0
- Python 3.12.8
**CMake configuration**
```sh
cmake -G "Ninja" \
-DCMAKE_TOOLCHAIN_FILE=../ClangToolChain.cmake \
-DCMAKE_BUILD_TYPE=Release \
-DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}" \
-DLINUX_x86_64-unknown-linux-gnu_SYSROOT="${INSTALL_DIR}/x86_64-linux/sys-root" \
-C ../clang/cmake/caches/BuildLlvmMultistage-stage2.cmake \
../llvm
ninja toolchain-distribution
install-toolchain-distribution-stripped
```
`BuildLlvmMultistage-stage2.cmake` is `clang/cmake/caches/Fuchsia-stage2.cmake` stripped of logic for handling targets other than x86_64-unknown-linux-gnu.
**Error**
During build of runtimes - more specifically rtsan following error is generated:
```
FAILED: compiler-rt/lib/rtsan/CMakeFiles/RTRtsan.x86_64.dir/rtsan_context.cpp.o
/src/llvm-project/build/./bin/clang++ --target=x86_64-unknown-linux-gnu --sysroot=/var/buildlibs/clang+llvm-20.1.0-rc2-x86_64-linux-gnu/x86_64-linux/sys-root -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/src/llvm-project/compiler-rt/lib/rtsan/.. --target=x86_64-unknown-linux-gnu -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -ffile-prefix-map=/src/llvm-project/build/runtimes/runtimes-x86_64-unknown-linux-gnu-bins=../../../ -ffile-prefix-map=/src/llvm-project/= -no-canonical-prefixes -Wall -Wno-unused-parameter -O3 -DNDEBUG -fPIC -fno-builtin -fno-exceptions -fomit-frame-pointer -funwind-tables -fno-stack-protector -fno-sanitize=safe-stack -fvisibility=hidden -fno-lto -Wthread-safety -Wthread-safety-reference -Wthread-safety-beta -O3 -gline-tables-only -Wno-gnu -Wno-variadic-macros -Wno-c99-extensions -ftrivial-auto-var-init=pattern -nostdinc++ -isystem/src/llvm-project/build/include/x86_64-unknown-linux-gnu/c++/v1 -isystem/src/llvm-project/build/include/c++/v1 -isystem/src/llvm-project/libcxxabi/include -DSANITIZER_COMMON_NO_REDEFINE_BUILTINS -fno-rtti -std=c++17 -MD -MT compiler-rt/lib/rtsan/CMakeFiles/RTRtsan.x86_64.dir/rtsan_context.cpp.o -MF compiler-rt/lib/rtsan/CMakeFiles/RTRtsan.x86_64.dir/rtsan_context.cpp.o.d -o compiler-rt/lib/rtsan/CMakeFiles/RTRtsan.x86_64.dir/rtsan_context.cpp.o -c /src/llvm-project/compiler-rt/lib/rtsan/rtsan_context.cpp
/src/llvm-project/compiler-rt/lib/rtsan/rtsan_context.cpp:16:10: fatal error: 'new' file not found
16 | #include <new>
| ^~~~~
1 error generated.
```
**Potential fix**
Based on the other [logs](https://github.com/theorian-solutions/cc_toolchain_builds/actions/runs/13379723543/job/37366343527#step:12:6272) seems like target `cxx-headers` is running at the same time as build of rtsan which depends on a header `new` already being copied to build output. Following patch fixed the issue for me:
```patch
---
compiler-rt/lib/rtsan/CMakeLists.txt | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/compiler-rt/lib/rtsan/CMakeLists.txt b/compiler-rt/lib/rtsan/CMakeLists.txt
index a4413d9992b6..40bcf7facad7 100644
--- a/compiler-rt/lib/rtsan/CMakeLists.txt
+++ b/compiler-rt/lib/rtsan/CMakeLists.txt
@@ -37,6 +37,11 @@ set(RTSAN_DYNAMIC_LIBS
${SANITIZER_CXX_ABI_LIBRARIES}
${SANITIZER_COMMON_LINK_LIBS})
+if(TARGET cxx-headers OR HAVE_LIBCXX)
+ # Rtsan uses C++ standard library headers.
+ set(RTSAN_DEPS cxx-headers)
+endif()
+
append_rtti_flag(OFF RTSAN_CFLAGS)
if(APPLE)
--
2.43.0
```
But not sure if it is going breaks building any other platform or use-case.
</pre>
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