What build variable determines where clang finds libclang_rt.builtins.a?

Runtimes
1

I make clang and runtimes builds using my own cmake cache file that I created a while ago looking at the ones provided for Fuchsia in clang/cmake/caches. I build with the following settings in my cache file:

  set(LLVM_BUILTIN_TARGETS "x86_64-unknown-linux-gnu;i386-unknown-linux-gnu" CACHE STRING "")
  set(LLVM_RUNTIME_TARGETS "x86_64-unknown-linux-gnu;i386-unknown-linux-gnu" CACHE STRING "")

macro(SetBoolForeachTarget Var Value)
  set(${Var} ${Value} CACHE BOOL "")
  foreach(T ${LLVM_RUNTIME_TARGETS})
    set(RUNTIMES_${T}_${Var} ${Value} CACHE BOOL "")
  endforeach()
endmacro()

SetBoolForeachTarget(COMPILER_RT_BUILD_BUILTINS ON)
SetBoolForeachTarget(COMPILER_RT_USE_BUILTINS_LIBRARY ON)

It has worked fine for me for multiple releases of LLVM and version 17.0.6 builds without any issues. But I am running into a problem building from trunk. The build fails when linking libc++.so (error is shown below).

ld.lld: error: cannot open /global/LLVM/build/llvm-build-main/x86_64/build-stage2/lib/clang/19/lib/linux/libclang_rt.builtins-i386.a: No such file or directory

It is looking for libclang_rt.builtins-i386.a in lib/clang/19/lib/linux. I am not sure why it is looking for it there instead of picking up lib/clang/19/lib/i386-unknown-linux-gnu/libclang_rt.builtins.a. Please note that this issue is there only with trunk and release/17 works fine (I have not checked 18 rc). What changed in trunk (19.0.0git) w.r.t. release/17 and if it is a problem with my cache file how should I change it to fix this failure?

I have uploaded my full cache file here

Here is the command line that fails during build:

FAILED: /global/LLVM/build/llvm-build-main/x86_64/build-stage2/lib/i386-unknown-linux-gnu/libc++.so.1.0
: && /global/LLVM/build/llvm-build-main/x86_64/build-stage2/./bin/clang++ --target=i386-unknown-linux-gnu -fPIC -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 -O3 -DNDEBUG  -Wl,-z,defs -Wl,-z,nodelete -fuse-ld=lld -Wl,--color-diagnostics -shared -Wl,-soname,libc++.so.1 -o /global/LLVM/build/llvm-build-main/x86_64/build-stage2/lib/i386-unknown-linux-gnu/libc++.so.1.0 libunwind/src/CMakeFiles/unwind_shared_objects.dir/libunwind.cpp.o libunwind/src/CMakeFiles/unwind_shared_objects.dir/Unwind-EHABI.cpp.o libunwind/src/CMakeFiles/unwind_shared_objects.dir/Unwind-seh.cpp.o libunwind/src/CMakeFiles/unwind_shared_objects.dir/UnwindLevel1.c.o libunwind/src/CMakeFiles/unwind_shared_objects.dir/UnwindLevel1-gcc-ext.c.o libunwind/src/CMakeFiles/unwind_shared_objects.dir/Unwind-sjlj.c.o libunwind/src/CMakeFiles/unwind_shared_objects.dir/Unwind-wasm.c.o libunwind/src/CMakeFiles/unwind_shared_objects.dir/UnwindRegistersRestore.S.o libunwind/src/CMakeFiles/unwind_shared_objects.dir/UnwindRegistersSave.S.o libcxx/src/CMakeFiles/cxx_shared.dir/algorithm.cpp.o libcxx/src/CMakeFiles/cxx_shared.dir/any.cpp.o libcxx/src/CMakeFiles/cxx_shared.dir/bind.cpp.o libcxx/src/CMakeFiles/cxx_shared.dir/call_once.cpp.o libcxx/src/CMakeFiles/cxx_shared.dir/charconv.cpp.o libcxx/src/CMakeFiles/cxx_shared.dir/chrono.cpp.o libcxx/src/CMakeFiles/cxx_shared.dir/error_category.cpp.o libcxx/src/CMakeFiles/cxx_shared.dir/exception.cpp.o libcxx/src/CMakeFiles/cxx_shared.dir/filesystem/filesystem_clock.cpp.o libcxx/src/CMakeFiles/cxx_shared.dir/filesystem/filesystem_error.cpp.o libcxx/src/CMakeFiles/cxx_shared.dir/filesystem/path.cpp.o ...
ld.lld: error: cannot open /global/LLVM/build/llvm-build-main/x86_64/build-stage2/lib/clang/19/lib/linux/libclang_rt.builtins-i386.a: No such file or directory
ld.lld: error: cannot open /global/LLVM/build/llvm-build-main/x86_64/build-stage2/lib/clang/19/lib/linux/libclang_rt.builtins-i386.a: No such file or directory
clang++: error: linker command failed with exit code 1 (use -v to see invocation)

Wonder if the issue discussed in this post is related.

UPDATE Another data point is that the build goes through if I do not build 32-bit runtimes. So this could be a problem with the clang driver.

2

I found that I was unintentionally setting COMPILER_RT_BUILD_BUILTINS and RUNTIMES_i386-unknown-linux-gnu_COMPILER_RT_BUILD_BUILTINS to ON, which causes libclang_rt.builtins.a to be re-built during the runtimes build. This will not work due to the known cyclic dependency between builtins and rest of runtimes.

The fix in my cache file is to set only COMPILER_RT_BUILD_BUILTINS to ON so that builtins are built before the rest of runtimes, but not again during runtimes.

I think the error from clang about libclang_rt.builtins-i386.a is because i386-unknown-linux-gnu/lib/libclang_rt.builtins.a was missing, presumably due to it getting regenerated by the runtimes build. I am not sure why the regeneration happens though, if an up-to-date libclang_rt.builtins.a from the earlier builtins build exists. In any case, removing the unnecessary RUNTIMES_<target>_COMPILER_RT_BUILD_BUILTINS seems to have fixed my issue.