[rust][rust_hello] Very basic Rust hello world app

This creates an very basic rust hello world app. The app declaration is
done through unsafe C, but this is sufficient to demonstrate building
and linking a rust app into LK.

Signed-off-by: David Brown <[email protected]>

Author: d3zd3z

app/rust_hello/Cargo.toml

@@ -0,0 +1,17 @@
+# Rust sample hello world application crate.
+
+[package]
+name = "rust_hello"
+version = "0.1.0"
+edition = "2024"
+description = """
+Rust LK hello world application.
+"""
+license = "MIT"
+
+[dependencies.lk]
+version = "0.1.0"
+path = "../../rust/lk"
+
+[dependencies.log]
+version = "0.4.27"

app/rust_hello/rules.mk

@@ -0,0 +1,10 @@
+LOCAL_DIR := $(GET_LOCAL_DIR)
+
+RUST_CRATES += $(LOCAL_DIR)
+$(info "Adding rust crate $(LOCAL_DIR)")
+
+MODULE := $(LOCAL_DIR)
+
+MODULES += $(MODULE)
+
+MODULE :=

app/rust_hello/src/lib.rs

@@ -0,0 +1,28 @@
+// Sample application.
+
+#![no_std]
+
+use core::ffi::c_void;
+
+use lk::sys::{APP_FLAG_NO_AUTOSTART, app_descriptor};
+
+pub fn must_link() {}
+
+/// Manual, and unsafe declration of an app.
+#[unsafe(link_section = "apps")]
+#[used]
+static APP_RUST_HELLO: app_descriptor = app_descriptor {
+    name: c"rust_hello".as_ptr(),
+    init: Some(init),
+    entry: Some(main),
+    flags: APP_FLAG_NO_AUTOSTART,
+    stack_size: 0,
+};
+
+extern "C" fn init(_desc: *const app_descriptor) {
+    log::info!("Rust hello app init");
+}
+
+extern "C" fn main(_desc: *const app_descriptor, _args: *mut c_void) {
+    log::info!("Rust hello app main");
+}

project/qemu-virt-arm64-test.mk

@@ -1,6 +1,7 @@
 # main project for qemu-aarch64
 MODULES += \
 	app/shell \
+	app/rust_hello \
     lib/uefi \
 
 include project/virtual/test.mk

rust/lk-sys/build.rs

@@ -58,6 +58,8 @@ fn main() -> anyhow::Result<()> {
         .allowlist_type("lk_init_struct")
         .allowlist_function("register_int_handler")
         .allowlist_function("unmask_interrupt")
+        .allowlist_type("app_descriptor")
+        .allowlist_item("APP_FLAG.*")
         .generate()?;
 
     bindings.write_to_file(out_path.join("bindings.rs"))?;

rust/lk-sys/src/lib.rs

@@ -15,6 +15,7 @@ use core::ffi::c_char;
 include!(concat!(env!("OUT_DIR"), "/bindings.rs"));
 
 unsafe impl Sync for lk_init_struct {}
+unsafe impl Sync for app_descriptor {}
 
 // lk_init_level constants have large gaps between them and some modules
 // add or subtract from these constants to indicate that it wants to run

rust/lk-sys/wrapper.h

@@ -28,4 +28,8 @@
 
 #include <platform/interrupts.h>
 
+#if WITH_APP
+#include <app.h>
+#endif
+
 // #include "error.h"