Merge pull request grpc#24992 from gnossen/fix_grpc_tools_so_mac_symbols

Fix visibility of libprotobuf symbols in protoc_compiler.so on Mac

tools/distrib/python/grpcio_tools/setup.py

@@ -44,6 +44,12 @@
 import protoc_lib_deps
 import grpc_version
 
+_EXT_INIT_SYMBOL = None
+if sys.version_info[0] == 2:
+    _EXT_INIT_SYMBOL = "init_protoc_compiler"
+else:
+    _EXT_INIT_SYMBOL = "PyInit__protoc_compiler"
+
 _parallel_compile_patch.monkeypatch_compile_maybe()
 
 CLASSIFIERS = [
@@ -118,6 +124,28 @@ def check_linker_need_libatomic():
         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.
+    #
+    # Finally, the leading underscore here is part of the Mach-O ABI. Unlike
+    # more modern ABIs (ELF et al.), Mach-O prepends an underscore to the names
+    # of C functions.
+    if "darwin" in sys.platform:
+        EXTRA_ENV_LINK_ARGS += ' -Wl,-exported_symbol,_{}'.format(
+            _EXT_INIT_SYMBOL)
     if "linux" in sys.platform or "darwin" in sys.platform:
         EXTRA_ENV_LINK_ARGS += ' -lpthread'
         if check_linker_need_libatomic():