[Linux] Only export extension init symbol

Since we link with static libstdc++ we need to tell gcc to only export
the necessary symbols.
Using "-fvisibility=hidden" will not work, since libstdc++ explicitly
export its symbols.

SConstruct

@@ -120,18 +120,6 @@ if env["platform"] == "macos" and os.environ.get("OSXCROSS_ROOT", ""):
     if env["macos_deployment_target"] != "default":
         env["ENV"]["MACOSX_DEPLOYMENT_TARGET"] = env["macos_deployment_target"]
 
-# Patch linux flags to statically link libgcc and libstdc++
-if env["platform"] == "linux":
-    env.Append(
-        LINKFLAGS=[
-            "-Wl,--no-undefined",
-            "-static-libgcc",
-            "-static-libstdc++",
-        ]
-    )
-    # And add some linux dependencies.
-    env.Append(LIBS=["pthread", "dl"])
-
 opts.Update(env)
 
 target = env["target"]
@@ -175,6 +163,23 @@ rtc = env.BuildLibDataChannel(ssl)
 # but it's better to be safe in case of indirect inclusions by one of our other dependencies.
 env.Depends(sources, ssl + rtc)
 
+# We want to statically link against libstdc++ on Linux to maximize compatibility, but we must restrict the exported
+# symbols using a GCC version script, or we might end up overriding symbols from other libraries.
+symbols_file = None
+if env["platform"] == "linux":
+    if env["godot_version"] == "3":
+        symbols_file = env.File("misc/dist/linux/symbols-gdnative.map")
+    else:
+        symbols_file = env.File("misc/dist/linux/symbols-extension.map")
+    env.Append(
+        LINKFLAGS=[
+            "-Wl,--no-undefined,--version-script=" + symbols_file.abspath,
+            "-static-libgcc",
+            "-static-libstdc++",
+        ]
+    )
+    env.Depends(sources, symbols_file)
+
 # Make the shared library
 result_name = "libwebrtc_native{}{}".format(env["suffix"], env["SHLIBSUFFIX"])
 if env["godot_version"] != "3" and env["platform"] == "macos":
@@ -190,6 +195,7 @@ if env["godot_version"] != "3" and env["platform"] == "macos":
     library = [library_file, plist_file]
 else:
     library = env.SharedLibrary(target=os.path.join(result_path, "lib", result_name), source=sources)
+
 Default(library)
 
 # GDNativeLibrary

misc/dist/linux/symbols-extension.map

@@ -0,0 +1,6 @@
+{
+    global:
+        webrtc_extension_init;
+    local:
+        *;
+};

misc/dist/linux/symbols-gdnative.map

@@ -0,0 +1,9 @@
+{
+    global:
+        godot_gdnative_singleton;
+        godot_gdnative_init;
+        godot_gdnative_terminate;
+        godot_nativescript_init;
+    local:
+        *;
+};

tools/openssl.py

@@ -125,6 +125,8 @@ def build_openssl(env, jobs=None):
         env.Prepend(LIBPATH=[env["SSL_BUILD"]])
         if env["platform"] == "windows":
             env.PrependUnique(LIBS=["crypt32", "ws2_32", "advapi32", "user32"])
+        if env["platform"] == "linux":
+            env.PrependUnique(LIBS=["pthread", "dl"])
         env.Prepend(LIBS=env["SSL_LIBS"])
         return [env["SSL_CRYPTO_LIBRARY"], env["SSL_LIBRARY"]]
 
@@ -169,6 +171,8 @@ def build_openssl(env, jobs=None):
     env.Prepend(LIBPATH=[env["SSL_BUILD"]])
     if env["platform"] == "windows":
         env.PrependUnique(LIBS=["crypt32", "ws2_32", "advapi32", "user32"])
+    if env["platform"] == "linux":
+        env.PrependUnique(LIBS=["pthread", "dl"])
     env.Prepend(LIBS=env["SSL_LIBS"])
 
     return ssl
@@ -223,8 +227,6 @@ def exists(env):
 
 
 def generate(env):
-    env.AddMethod(build_openssl, "OpenSSL")
-
     # Check if the user specified infos about external OpenSSL files.
     external_opts = ["openssl_external_crypto", "openssl_external_ssl", "openssl_external_include"]
     is_set = lambda k: env.get(k, "") != ""

tools/rtc.py

@@ -37,6 +37,8 @@ def build_library(env, ssl):
     # Configure env.
     if env["platform"] == "windows":
         env.PrependUnique(LIBS=["iphlpapi", "bcrypt"])
+    if env["platform"] == "linux":
+        env.PrependUnique(LIBS=["pthread"])
     env.Prepend(LIBS=list(filter(lambda f: str(f).endswith(lib_ext), rtc)))
     env.Append(CPPPATH=["#thirdparty/libdatachannel/include"])