examples: New app to build Rust with Cargo

Build Rust applictions with cargo is the most commn way,
and it's more easy to cooporate with Rust ecosystem.

This example shows how to use cargo to build a simple hello world
application.

And please notice that you need to install nighly version of rustc
to support this feature, any version after rust-lang/rust#127755
is merged, can use NuttX as cargo target directly.

Build
-----

To build hello_rust_cargo application, you can use any target that based
on RISCV32IMAC, for example:
```
cmake -B build -DBOARD_CONFIG=rv-virt:nsh -GNinja .
```

And disable ARCH_FPU in menuconfig, since the hard coded target triple
in this demo is `riscv32imac`.

TODO:
1. Add support for Rust in CMake based system
2. Upstream https://github.com/no1wudi/libc to rust-lang/libc
3. Port libstd of Rust to NuttX, which blocked by 2.

examples/hello_rust_cargo/CMakeLists.txt

@@ -0,0 +1,51 @@
+# ##############################################################################
+# apps/examples/hello_rust_cargo/CMakeLists.txt
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more contributor
+# license agreements.  See the NOTICE file distributed with this work for
+# additional information regarding copyright ownership.  The ASF licenses this
+# file to you under the Apache License, Version 2.0 (the "License"); you may not
+# use this file except in compliance with the License.  You may obtain a copy of
+# the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+# License for the specific language governing permissions and limitations under
+# the License.
+#
+# ##############################################################################
+
+# Call cargo build from CMakeLists and add it to the build system.
+# Notice we should call cargo build with add_custom_target, otherwise
+# cargo will be called every time when cmake is configured.
+
+add_custom_target(cargo-build ALL
+    COMMAND cargo build --release
+      -Zbuild-std=core
+      --manifest-path ${CMAKE_CURRENT_SOURCE_DIR}/hello/Cargo.toml
+      --target riscv32imac-unknown-nuttx-elf
+)
+
+# Let target apps depends on cargo-build, so that cargo will be called before
+# building the target.
+add_dependencies(apps cargo-build)
+
+# Add static library apps/examples/hello_rust_cargo/hello/target/riscv32imac-unknown-nuttx-elf/release/libhello.a
+# to the build system.
+nuttx_library_import(hello ${CMAKE_CURRENT_SOURCE_DIR}/hello/target/riscv32imac-unknown-nuttx-elf/release/libhello.a)
+nuttx_add_extra_library(hello)
+
+if(CONFIG_EXAMPLES_HELLO_RUST_CARGO)
+  nuttx_add_application(
+    NAME
+    ${CONFIG_EXAMPLES_HELLO_RUST_CARGO_PROGNAME}
+    SRCS
+    proxy_main.c
+    STACKSIZE
+    ${CONFIG_EXAMPLES_HELLO_STACKSIZE}
+    PRIORITY
+    ${CONFIG_EXAMPLES_HELLO_PRIORITY})
+endif()

examples/hello_rust_cargo/Kconfig

@@ -0,0 +1,29 @@
+#
+# For a description of the syntax of this configuration file,
+# see the file kconfig-language.txt in the NuttX tools repository.
+#
+
+config EXAMPLES_HELLO_RUST_CARGO
+	tristate "\"Hello, Rust!\" example with Cargo"
+	default n
+	---help---
+		Enable the \"Hello, Rust!\" example using Cargo to build.
+
+if EXAMPLES_HELLO_RUST_CARGO
+
+config EXAMPLES_HELLO_RUST_CARGO_PROGNAME
+	string "Program name"
+	default "hello_rust_cargo"
+	---help---
+		This is the name of the program that will be used when the
+		program is installed.
+
+config EXAMPLES_HELLO_RUST_CARGO_PRIORITY
+	int "Hello Rust task priority"
+	default 100
+
+config EXAMPLES_HELLO_RUST_CARGO_STACKSIZE
+	int "Hello Rust stack size"
+	default DEFAULT_TASK_STACKSIZE
+
+endif

examples/hello_rust_cargo/Make.defs

@@ -0,0 +1,23 @@
+############################################################################
+# apps/examples/hello_rust_cargo/Make.defs
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.  The
+# ASF licenses this file to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance with the
+# License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+# License for the specific language governing permissions and limitations
+# under the License.
+#
+############################################################################
+
+ifneq ($(CONFIG_EXAMPLES_HELLO_RUST_CARGO),)
+CONFIGURED_APPS += $(APPDIR)/examples/hello_rust_cargo
+endif

examples/hello_rust_cargo/Makefile

@@ -0,0 +1,32 @@
+############################################################################
+# apps/examples/hello_rust/Makefile
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.  The
+# ASF licenses this file to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance with the
+# License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+# License for the specific language governing permissions and limitations
+# under the License.
+#
+############################################################################
+
+include $(APPDIR)/Make.defs
+
+# Hello, Rust! built-in application info
+
+PROGNAME  = $(CONFIG_EXAMPLES_HELLO_RUST_CARGO_PROGNAME)
+PRIORITY  = $(CONFIG_EXAMPLES_HELLO_RUST_CARGO_PRIORITY)
+STACKSIZE = $(CONFIG_EXAMPLES_HELLO_RUST_CARGO_STACKSIZE)
+MODULE    = $(CONFIG_EXAMPLES_HELLO_RUST_CARGO)
+
+# Do not suppport building this application from Makefile.
+
+include $(APPDIR)/Application.mk

examples/hello_rust_cargo/hello/.gitignore

@@ -0,0 +1 @@
+target

examples/hello_rust_cargo/hello/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "hello"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+crate-type = ["staticlib"]
+
+[dependencies]
+libc = { git = "https://github.com/no1wudi/libc", branch = "libc-0.2" }
+
+[profile.dev]
+panic ="abort"
+
+# Special hanlding for the panic! macro, can be removed once
+# the libstd port for NuttX is complete.
+[profile.release]
+panic ="abort"

examples/hello_rust_cargo/hello/src/lib.rs

@@ -0,0 +1,22 @@
+// no-std libraray for the Rust programming language
+#![no_std]
+
+extern crate libc;
+
+// Function hello_rust_cargo without manglng
+#[no_mangle]
+pub extern "C" fn rust_main() {
+    // Print hello world to stdout
+    unsafe {
+        libc::printf(
+            "Hello World from Rust build with Cargo!\n\0"
+                .as_ptr()
+                .cast(),
+        );
+    }
+}
+
+#[panic_handler]
+fn panic(_info: &core::panic::PanicInfo) -> ! {
+    loop {}
+}

examples/hello_rust_cargo/proxy_main.c

@@ -0,0 +1,42 @@
+/****************************************************************************
+ * apps/examples/hello_rust_cargo/proxy_main.c
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+#include <stdio.h>
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+extern void rust_main(void);
+
+/****************************************************************************
+ * main
+ ****************************************************************************/
+
+int main(int argc, FAR char *argv[])
+{
+  rust_main();
+  return 0;
+}