Add ppc64le/ppc64 architecture support

Add build support for ppc64le (little-endian, POWER8+) and ppc64
(big-endian, POWER5+) architectures:

- CMake architecture detection, compiler flags (-mcpu), and NaCl build
  defines for ppc64el/ppc64
- NACL_RUNTIME_ARCH allowlist and DAEMON_NACL_RUNTIME_ENABLED define to
  track whether a NaCl loader exists for the target architecture
- vm.nacl.available ROM cvar so the UI can detect NaCl availability
- Sys::Error when attempting to launch a NaCl VM on a platform without
  a NaCl loader, advising to use native DLL mode with devmap

Author: runlevel5

cmake/DaemonArchitecture.cmake

@@ -91,6 +91,12 @@ endif()
 
 daemon_add_buildinfo("char*" "DAEMON_NACL_ARCH_STRING" "\"${NACL_ARCH}\"")
 
+# NaCl runtime is only available on architectures that have a NaCl loader.
+set(NACL_RUNTIME_ARCH amd64 i686 armhf)
+if (NACL_ARCH IN_LIST NACL_RUNTIME_ARCH)
+	add_definitions(-DDAEMON_NACL_RUNTIME_ENABLED)
+endif()
+
 option(USE_ARCH_INTRINSICS "Enable custom code using intrinsics functions or asm declarations" ON)
 mark_as_advanced(USE_ARCH_INTRINSICS)
 
@@ -111,6 +117,7 @@ set_arch_intrinsics(${ARCH})
 
 set(amd64_PARENT "i686")
 set(arm64_PARENT "armhf")
+set(ppc64el_PARENT "ppc64")
 
 if (${ARCH}_PARENT)
 	set_arch_intrinsics(${${ARCH}_PARENT})

cmake/DaemonFlags.cmake

@@ -659,6 +659,18 @@ elseif (NOT NACL)
 		set(GCC_GENERIC_ARCH "armv6")
 		# There is no generic tuning option for armv6.
 		unset(GCC_GENERIC_TUNE)
+	elseif (ARCH STREQUAL "ppc64el")
+		# POWER8 minimum (first little-endian POWER).
+		# GCC uses -mcpu instead of -march/-mtune for POWER.
+		unset(GCC_GENERIC_ARCH)
+		unset(GCC_GENERIC_TUNE)
+		set(GCC_GENERIC_CPU "power8")
+	elseif (ARCH STREQUAL "ppc64")
+		# POWER5 minimum (first 64-bit POWER in wide use).
+		# GCC uses -mcpu instead of -march/-mtune for POWER.
+		unset(GCC_GENERIC_ARCH)
+		unset(GCC_GENERIC_TUNE)
+		set(GCC_GENERIC_CPU "power5")
 	else()
 		message(WARNING "Unknown architecture ${ARCH}")
 	endif()
@@ -676,6 +688,11 @@ elseif (NOT NACL)
 		if (GCC_GENERIC_TUNE)
 			try_c_cxx_flag_werror(MTUNE "-mtune=${GCC_GENERIC_TUNE}")
 		endif()
+
+		# POWER architectures use -mcpu instead of -march/-mtune.
+		if (GCC_GENERIC_CPU)
+			try_c_cxx_flag_werror(MCPU "-mcpu=${GCC_GENERIC_CPU}")
+		endif()
 	endif()
 
 	if (USE_CPU_RECOMMENDED_FEATURES)

cmake/DaemonNacl.cmake

@@ -71,6 +71,11 @@ else()
     add_definitions( -DNACL_BUILD_SUBARCH=32 )
   elseif( NACL_ARCH STREQUAL "armhf" )
     add_definitions( -DNACL_BUILD_ARCH=arm )
+  elseif( NACL_ARCH STREQUAL "ppc64el" OR NACL_ARCH STREQUAL "ppc64" )
+    # NaCl does not support PPC, but these defines must be set for native
+    # builds. Use dummy x86 values as PNaCl does for arch-independent builds.
+    add_definitions( -DNACL_BUILD_ARCH=x86 )
+    add_definitions( -DNACL_BUILD_SUBARCH=64 )
   else()
     message(WARNING "Unknown architecture ${NACL_ARCH}")
   endif()

src/engine/framework/VirtualMachine.cpp

@@ -88,6 +88,18 @@ static Cvar::Cvar<int> vm_timeout(
 	"Receive timeout in seconds",
 	Cvar::NONE, 2);
 
+#if defined(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
@@ -497,6 +509,13 @@ void VMBase::Create()
 	std::pair<IPC::Socket, IPC::Socket> pair = IPC::Socket::CreatePair();
 
 	IPC::Socket rootSocket;
+#if !defined(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) {