Fix visibility of libprotobuf symbols in protoc_compiler.so on Mac

tools/distrib/python/grpcio_tools/setup.py

@@ -118,6 +118,23 @@ if EXTRA_ENV_COMPILE_ARGS is None:
         EXTRA_ENV_COMPILE_ARGS += ' -fno-wrapv -frtti'
 if EXTRA_ENV_LINK_ARGS is None:
     EXTRA_ENV_LINK_ARGS = ''
+    # NOTE(rbellevi): Clang on Mac OS will make all static symbols (both variables
+    # and objects) global weak symbols. When a process loads the
+    # protobuf wheel's shared object library before loading *this* C extension,
+    # the runtime linker will prefer the protobuf module's version of symbols. This
+    # results in the process using a mixture of symbols from the protobuf wheel and
+    # this wheel, which may be using different versions of libprotobuf. In the case
+    # that they *are* using different versions of libprotobuf *and* there has been a
+    # change in data layout (or in other invariants) segfaults, data corruption, or
+    # "bad things" may happen.
+    #
+    # This flag ensures that on Mac, the only global symbol is the one loaded by the
+    # Python interpreter. The problematic global weak symbols become local weak symbols.
+    # This is not required on Linux since the compiler does not produce global weak
+    # symbols. This is not required on Windows as our ".pyd" file does not contain any
+    # symbols.
+    if "darwin" in sys.platform:
+        EXTRA_ENV_LINK_ARGS += ' -Wl,-exported_symbol,_PyInit__protoc_compiler'
     if "linux" in sys.platform or "darwin" in sys.platform:
         EXTRA_ENV_LINK_ARGS += ' -lpthread'
         if check_linker_need_libatomic():