ANDROID: rust_binder: add Rust Binder to Makefile

For now, we only provide the option to only enable C Binder, or to
enable both drivers. When both drivers are enabled, C Binder is always
the default.

We define a separate rust_binder-objs with all of the compilation units
rather than just listing them under obj-$(ANDROID_BINDER_IPC_RUST)
because otherwise five different GKI modules are built when choosing =m
for the config option.

With this commit, Rust Binder works as a built-in module. However it is
not actually enough to use it as a GKI module because GKI modules are
loaded too late in the boot process. That issue is tracked by
b/402049944 and will be fixed in a follow-up.

Bug: 388786466
Change-Id: I04a0b604a756717fff730e6e3eb4496da016a8e5
Signed-off-by: Alice Ryhl <aliceryhl@google.com>

drivers/android/Kconfig

@@ -37,6 +37,18 @@ config ANDROID_BINDER_DEVICES
 	  created. Each binder device has its own context manager, and is
 	  therefore logically separated from the other devices.
 
+config ANDROID_BINDER_IPC_RUST
+	tristate "Rust version of Android Binder IPC Driver"
+	depends on RUST && ANDROID_BINDER_IPC && ANDROID_BINDERFS
+	help
+	  This enables the Rust implementation of the Binder driver. At this
+	  time, the Rust implementation can only be built as an alternative to
+	  the C implementation. By default, the C implementation is used, but
+	  if the binder.impl=rust kernel command-line parameter is provided,
+	  then the Rust implementation is used instead.
+
+	  To build this as a GKI module, choose m.
+
 config ANDROID_BINDER_IPC_SELFTEST
 	bool "Android Binder IPC Driver Selftest"
 	depends on ANDROID_BINDER_IPC

drivers/android/Makefile

@@ -6,3 +6,7 @@ obj-$(CONFIG_ANDROID_BINDER_IPC)	+= binder.o binder_alloc.o
 obj-$(CONFIG_ANDROID_BINDER_IPC_SELFTEST) += binder_alloc_selftest.o
 obj-$(CONFIG_ANDROID_VENDOR_HOOKS) += vendor_hooks.o
 obj-$(CONFIG_ANDROID_DEBUG_KINFO)	+= debug_kinfo.o
+
+obj-$(CONFIG_ANDROID_BINDER_IPC_RUST)	+= rust_binder.o
+rust_binder-objs := binder/rust_binder.o binder/rust_binderfs.o binder/rust_binder_events.o
+rust_binder-objs += binder/rust_binder_hooks.o binder/page_range_helper.o

drivers/android/binder/rust_binder.rs

@@ -314,6 +314,8 @@ impl kernel::Module for BinderModule {
             }
         }
 
+        pr_warn!("Loaded Rust Binder.");
+
         BINDER_SHRINKER.register(kernel::c_str!("android-binder"))?;
 
         // SAFETY: The module is being loaded, so we can initialize binderfs.