Introduce symbol versioning for clang-cpp

The situation that required symbol versions on the LLVM shared library
can also happen for clang-cpp, although it is less common: different
tools require different versions of the library, and through transitive
dependencies a process ends up with multiple copies of clang-cpp. This
causes havoc with ELF, because calls meant to go one version of the
library end up with another.

I've also considered introducing a symbol version globally, but for
example the clang (C) library and other targets outside of LLVM/Clang,
e.g. libc++, would not want that. So it's probably best if we keep it to
those libraries.

Author: aaronpuchert

clang/tools/clang-shlib/CMakeLists.txt

@@ -48,6 +48,14 @@ add_clang_library(clang-cpp
                   ${_OBJECTS}
                   LINK_LIBS
                   ${_DEPS})
+
+configure_file(simple_version_script.map.in simple_version_script.map)
+
+if (NOT LLVM_LINKER_IS_SOLARISLD AND NOT MINGW)
+  # Solaris ld does not accept global: *; so there is no way to version *all* global symbols
+  target_link_options(clang-cpp PRIVATE LINKER:--version-script,${CMAKE_CURRENT_BINARY_DIR}/simple_version_script.map)
+endif()
+
 # Optimize function calls for default visibility definitions to avoid PLT and
 # reduce dynamic relocations.
 if (NOT APPLE AND NOT MINGW AND NOT LLVM_LINKER_IS_SOLARISLD_ILLUMOS)

clang/tools/clang-shlib/simple_version_script.map.in

@@ -0,0 +1 @@
+@LLVM_SHLIB_SYMBOL_VERSION@ { global: *; };

llvm/CMakeLists.txt

@@ -27,7 +27,7 @@ if (NOT PACKAGE_VERSION)
 endif()
 
 if(NOT DEFINED LLVM_SHLIB_SYMBOL_VERSION)
-  # "Symbol version prefix for libLLVM.so"
+  # "Symbol version prefix for libLLVM.so and libclang-cpp.so"
   set(LLVM_SHLIB_SYMBOL_VERSION "LLVM_${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}")
 endif()