[PATCH] D31639: [CMake][libcxxabi] Use -nodefaultlibs for CMake checks

[Kazushi Marukawa via Phabricator via llvm-commits]

kaz7 added a comment.

Hi, I have a question about this patch.  I appreciate any answers.  Thanks!



================
Comment at: libcxxabi/trunk/cmake/config-ix.cmake:26
+    find_compiler_rt_library(builtins LIBCXXABI_BUILTINS_LIBRARY)
+    list(APPEND CMAKE_REQUIRED_LIBRARIES "${LIBCXXABI_BUILTINS_LIBRARY}")
+  elseif (LIBCXXABI_HAS_GCC_S_LIB)
----------------
Hi!

Is it possible to ask about this implementation?

I'm trying to build `libcxxabi.so` and `libclang_rt.builtins-ve.a` for VE architecture.  However, generated `libcxxabi.so` requires `libclang_rt.builtins-ve.a` for `__multi3` function.  Then, ld causes following errors, when I compile any c++ test programs using generated `clang++`, `libc++.so`, `libcxxabi.so`, and `libclang_rt.builtins-ve.a`.  I think that this is an error trying to refer `__multi3` function in `libclang_rt.builtins-ve.a` from `libcxxabi.so`.
```
/opt/nec/ve/bin/nld: cmTC_f428b: hidden symbol `__veabi_multi3' in /home/jam/llvm-upstream/install/lib/clang/12.0.0/lib/linux/libclang_rt.builtins-ve.a(multi3.c.o) is referenced by DSO
    /opt/nec/ve/bin/nld: final link failed: Bad value
```

In order to solve this problem, I can add following CMakefile code to link `libcxxabi.so` with `libclang_rt.builtins-ve.a` at build-time.  It works fine for VE.  But, I'm not sure whther this modification works for all other architectures or not.  Or, I guess, there is better answer for this problem.
```
     list(APPEND CMAKE_REQUIRED_FLAGS -rtlib=compiler-rt)
     find_compiler_rt_library(builtins LIBCXXABI_BUILTINS_LIBRARY)
     list(APPEND CMAKE_REQUIRED_LIBRARIES "${LIBCXXABI_BUILTINS_LIBRARY}")
+    # CMAKE_REQUIRED_LIBRARIES is not used to link libc++abi.so, so
+    # append builtins to LIBCXXABI_SHARED_LIBRARIES too
+    list(APPEND LIBCXXABI_SHARED_LIBRARIES "${LIBCXXABI_BUILTINS_LIBRARY}")
```

I appreciate if you have any suggestions for me here.  Thanks!


Repository:
  rL LLVM

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  https://reviews.llvm.org/D31639/new/

https://reviews.llvm.org/D31639