[clang] [llvm] Introduce symbol versioning for clang-cpp (PR #116556)

[Aaron Puchert via cfe-commits]

https://github.com/aaronpuchert created https://github.com/llvm/llvm-project/pull/116556

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.

>From c7c190d0809bc8fe86e04d1ff4d6719d7acdcbe2 Mon Sep 17 00:00:00 2001
From: Aaron Puchert <aaronpuchert at alice-dsl.net>
Date: Sun, 17 Nov 2024 21:17:35 +0100
Subject: [PATCH] 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.
---
 clang/tools/clang-shlib/CMakeLists.txt               | 8 ++++++++
 clang/tools/clang-shlib/simple_version_script.map.in | 1 +
 llvm/CMakeLists.txt                                  | 2 +-
 3 files changed, 10 insertions(+), 1 deletion(-)
 create mode 100644 clang/tools/clang-shlib/simple_version_script.map.in

diff --git a/clang/tools/clang-shlib/CMakeLists.txt b/clang/tools/clang-shlib/CMakeLists.txt
index 298d3a9d18fec8..830f2b138ffa16 100644
--- a/clang/tools/clang-shlib/CMakeLists.txt
+++ b/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)
diff --git a/clang/tools/clang-shlib/simple_version_script.map.in b/clang/tools/clang-shlib/simple_version_script.map.in
new file mode 100644
index 00000000000000..cb2306d1f59682
--- /dev/null
+++ b/clang/tools/clang-shlib/simple_version_script.map.in
@@ -0,0 +1 @@
+ at LLVM_SHLIB_SYMBOL_VERSION@ { global: *; };
diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index cde4a999ea2e74..304197667dad6e 100644
--- a/llvm/CMakeLists.txt
+++ b/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()