Add NaCl availability cvar and block remote server joins on non-NaCl platforms

- Add vm.nacl.available ROM cvar (true on amd64/i686/armhf, false otherwise)
  so the UI can detect NaCl availability at runtime
- Default vm.cgame.type and vm.sgame.type to native DLL (3) on platforms
  without NaCl runtime, instead of NaCl (0) which would fail
- Block joining remote servers on non-NaCl platforms in CL_InitCGame()
  since loading local (unsandboxed) game code instead of the server's
  NaCl modules is considered cheating
- Move Sys::Error guard from early in VMBase::Create() to just before the
  CreateNaClVM dispatch as a secondary safety net

Author: runlevel5

src/engine/client/cl_cgame.cpp

@@ -593,6 +593,18 @@ Should only by called by CL_StartHunkUsers
 */
 void CL_InitCGame()
 {
+#ifndef DAEMON_NACL_RUNTIME_ENABLED
+	// NaCl sandbox is not available on this platform. Joining a remote server
+	// would load local (unsandboxed) game code instead of the server's NaCl
+	// modules, which is considered cheating. Only local games (via devmap,
+	// which enables cheats) are allowed.
+	if ( !NET_IsLocalAddress( clc.serverAddress ) )
+	{
+		Sys::Error( "Cannot join remote servers: NaCl sandbox is not available on this platform.\n"
+		            "You can host a local game using devmap (the server creation menu does this automatically)." );
+	}
+#endif
+
 	const char *info;
 	const char *mapname;
 	int        t1, t2;

src/engine/framework/VirtualMachine.cpp

@@ -88,6 +88,18 @@ static Cvar::Cvar<int> vm_timeout(
 	"Receive timeout in seconds",
 	Cvar::NONE, 2);
 
+#ifdef DAEMON_NACL_RUNTIME_ENABLED
+static Cvar::Cvar<bool> vm_nacl_available(
+	"vm.nacl.available",
+	"Whether NaCl runtime is available on this platform",
+	Cvar::ROM, true);
+#else
+static Cvar::Cvar<bool> vm_nacl_available(
+	"vm.nacl.available",
+	"Whether NaCl runtime is available on this platform",
+	Cvar::ROM, false);
+#endif
+
 namespace VM {
 
 // https://github.com/Unvanquished/Unvanquished/issues/944#issuecomment-744454772
@@ -479,14 +491,6 @@ void VMBase::Create()
 	if (type < TYPE_BEGIN || type >= TYPE_END)
 		Sys::Drop("VM: Invalid type %d", type);
 
-#ifndef DAEMON_NACL_RUNTIME_ENABLED
-	if (type == TYPE_NACL || type == TYPE_NACL_LIBPATH) {
-		Sys::Error("VM: NaCl is not available on this platform. "
-		           "NaCl is required for online games. "
-		           "To play offline with native DLLs, set vm.cgame.type, vm.sgame.type to 3");
-	}
-#endif
-
 	int loadStartTime = Sys::Milliseconds();
 
 	// Free the VM if it exists
@@ -505,6 +509,13 @@ void VMBase::Create()
 	std::pair<IPC::Socket, IPC::Socket> pair = IPC::Socket::CreatePair();
 
 	IPC::Socket rootSocket;
+#ifndef DAEMON_NACL_RUNTIME_ENABLED
+	if (type == TYPE_NACL || type == TYPE_NACL_LIBPATH) {
+		Sys::Error("NaCl VM is not supported on this platform. "
+		           "Set vm.cgame.type and vm.sgame.type to 3 (native DLL) "
+		           "and use devmap instead of map.");
+	}
+#endif
 	if (type == TYPE_NACL || type == TYPE_NACL_LIBPATH) {
 		std::tie(processHandle, rootSocket) = CreateNaClVM(std::move(pair), name, params.debug.Get(), type == TYPE_NACL, params.debugLoader.Get());
 	} else if (type == TYPE_NATIVE_EXE) {

src/engine/framework/VirtualMachine.h

@@ -95,8 +95,13 @@ enum vmType_t {
 struct VMParams {
 	VMParams(std::string name, int vmTypeFlags)
 		: logSyscalls("vm." + name + ".logSyscalls", "dump all the syscalls in the " + name + ".syscallLog file", Cvar::NONE, false),
+#ifdef DAEMON_NACL_RUNTIME_ENABLED
 		  vmType("vm." + name + ".type", "how the vm should be loaded for " + name, vmTypeFlags,
 		         Util::ordinal(vmType_t::TYPE_NACL), 0, Util::ordinal(vmType_t::TYPE_END) - 1),
+#else
+		  vmType("vm." + name + ".type", "how the vm should be loaded for " + name, vmTypeFlags,
+		         Util::ordinal(vmType_t::TYPE_NATIVE_DLL), 0, Util::ordinal(vmType_t::TYPE_END) - 1),
+#endif
 		  debug("vm." + name + ".debug", "run a gdbserver on localhost:4014 to debug the VM", Cvar::NONE, false),
 		  debugLoader("vm." + name + ".debugLoader", "make nacl_loader dump information to " + name + "-nacl_loader.log", Cvar::NONE, 1, 0, 5) {
 	}
@@ -111,7 +116,11 @@ struct VMParams {
 class VMBase {
 public:
 	VMBase(std::string name_, int vmTypeCvarFlags)
+#ifdef DAEMON_NACL_RUNTIME_ENABLED
 		: processHandle(Sys::INVALID_HANDLE), name(name_), type(TYPE_NACL), params(name_, vmTypeCvarFlags) {}
+#else
+		: processHandle(Sys::INVALID_HANDLE), name(name_), type(TYPE_NATIVE_DLL), params(name_, vmTypeCvarFlags) {}
+#endif
 
 	// Create the VM for the named module. This will automatically free any existing VM.
 	void Create();