Create components for Rust and C integration (#10)

* Create components for Rust and C integration
* Create component for C code that will be callable from Rust
* Create component for Rust code that will be callable from C
* Remove circular dependencies between C and Rust code
* Run cbindgen to dynamically generate C headers for Rust functions

CMakeLists.txt

@@ -4,10 +4,3 @@ cmake_minimum_required(VERSION 3.5)
 
 include($ENV{IDF_PATH}/tools/cmake/project.cmake)
 project(esp32-hello-rust)
-
-# The Xtensa Rust build includes compiler intrinsics that conflict with names
-# in GCC. To avoid multiple definition errors, allow the linker to pick one of
-# the available options and ignore the others.
-if((${IDF_TARGET} MATCHES "esp32") OR (${IDF_TARGET} MATCHES "esp32s2"))
-    target_link_options(${CMAKE_PROJECT_NAME}.elf PRIVATE "-Wl,--allow-multiple-definition")
-endif()

components/clib/CMakeLists.txt

@@ -0,0 +1,2 @@
+idf_component_register(SRCS "clib.c"
+                    INCLUDE_DIRS "include")

components/clib/README.md

@@ -0,0 +1,5 @@
+# clib
+
+This component exposes functions and data defined in C that will accessed from Rust.
+
+The Rust build will automatically generate bindings to these functions by processing the exported header files with bindgen.

components/clib/clib.c

@@ -0,0 +1,17 @@
+/* Hello World Example
+
+   This example code is in the Public Domain (or CC0 licensed, at your option.)
+
+   Unless required by applicable law or agreed to in writing, this
+   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+   CONDITIONS OF ANY KIND, either express or implied.
+*/
+#include <stdio.h>
+
+#include "CApi.h"
+
+bool validate_param_in_c(int param, int value)
+{
+    printf("C validated param #%d = %d\n", param, value);
+    return true;
+}

components/rustlib/CMakeLists.txt

@@ -0,0 +1,57 @@
+set(RUST_DEPS "clib")
+
+idf_component_register(
+    SRCS "placeholder.c"
+    INCLUDE_DIRS ""
+    PRIV_REQUIRES "${RUST_DEPS}"
+)
+
+set(CARGO_BUILD_TYPE "release")
+set(CARGO_BUILD_ARG "--release")
+if(CONFIG_IDF_TARGET_ARCH_RISCV)
+    set(CARGO_TARGET "riscv32i-unknown-none-elf")
+    set(CARGO_FEATURES_ARG "")
+elseif(CONFIG_IDF_TARGET_ARCH_XTENSA)
+    set(CARGO_TARGET "xtensa-esp32-none-elf")
+    set(CARGO_FEATURES_ARG "--features=std")
+endif()
+
+set(RUST_PROJECT_DIR "${CMAKE_CURRENT_LIST_DIR}")
+set(RUST_BUILD_DIR "${CMAKE_CURRENT_BINARY_DIR}")
+set(RUST_TARGET_DIR "${RUST_BUILD_DIR}/target")
+set(RUST_INCLUDE_DIR "${RUST_TARGET_DIR}")
+set(RUST_INCLUDE_HEADER "${RUST_INCLUDE_DIR}/RustApi.h")
+set(RUST_STATIC_LIBRARY "${RUST_TARGET_DIR}/${CARGO_TARGET}/${CARGO_BUILD_TYPE}/librustlib.a")
+
+ExternalProject_Add(
+    rustlib_project
+    PREFIX "${RUST_PROJECT_DIR}"
+    DOWNLOAD_COMMAND ""
+    CONFIGURE_COMMAND ${CMAKE_COMMAND} -E env
+        CARGO_BUILD_TARGET=${CARGO_TARGET}
+        CARGO_BUILD_TARGET_DIR=${RUST_TARGET_DIR}
+        cargo clean
+    BUILD_COMMAND ${CMAKE_COMMAND} -E env
+        CARGO_BUILD_TARGET=${CARGO_TARGET}
+        CARGO_BUILD_TARGET_DIR=${RUST_TARGET_DIR}
+        cargo build ${CARGO_BUILD_ARG} ${CARGO_FEATURES_ARG}
+    INSTALL_COMMAND ""
+    BUILD_ALWAYS TRUE
+    TMP_DIR "${RUST_BUILD_DIR}/tmp"
+    STAMP_DIR "${RUST_BUILD_DIR}/stamp"
+    DOWNLOAD_DIR "${RUST_BUILD_DIR}"
+    SOURCE_DIR "${RUST_PROJECT_DIR}"
+    BINARY_DIR "${RUST_PROJECT_DIR}"
+    INSTALL_DIR "${RUST_BUILD_DIR}"
+    BUILD_BYPRODUCTS
+        "${RUST_INCLUDE_HEADER}"
+        "${RUST_STATIC_LIBRARY}"
+)
+
+set_source_files_properties("${RUST_INCLUDE_HEADER}" PROPERTIES GENERATED true)
+
+add_prebuilt_library(rustlib_lib "${RUST_STATIC_LIBRARY}" PRIV_REQUIRES "${RUST_DEPS}")
+add_dependencies(rustlib_lib rustlib_project)
+
+target_include_directories(${COMPONENT_LIB} PUBLIC "${RUST_INCLUDE_DIR}")
+target_link_libraries(${COMPONENT_LIB} PRIVATE rustlib_lib)

components/rustlib/Cargo.toml

@@ -6,10 +6,10 @@ edition = "2018"
 
 [lib]
 crate-type = ["staticlib"]
-#crate-type = ["rlib", "staticlib"]
 
 [build-dependencies]
 bindgen = "0.58"
+cbindgen = "0.19"
 
 [features]
 std = []

components/rustlib/README.md

@@ -0,0 +1,13 @@
+# rustlib
+
+This component generates a static library from Rust source code and exposes functions that will be callable from the main IDF application from C.
+
+This component is responsible for three separate functions:
+
+* Export C bindings for Rust functions with `cbindgen`.
+* Import Rust binding for C functions with `bindgen`.
+* Build a top level static library from Rust code. The `cargo` build command is wrapped in a CMake `ExternalProject_Add` command.
+
+Currently the `build.rs` script expects the `clib` component to export a header with the name `CApi.h`. If the name of the include file changes or if more files are added, the build script must be updated to process the latest headers.
+
+Depending on the complexity of the project, the `cbindgen` and `bindgen` steps could be broken out into one or more IDF components or Rust crates. However, to prevent redundant duplication of the Rust runtime, all Rust crates should be compiled into a single static library that will be linked into the final IDF application.

components/rustlib/build.rs

@@ -5,19 +5,32 @@ fn main() {
     let target = env::var("TARGET").unwrap();
 
     let cargo_dir = PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap());
+    let target_dir = PathBuf::from(env::var("CARGO_BUILD_TARGET_DIR").unwrap());
     let out_dir = PathBuf::from(env::var("OUT_DIR").unwrap());
 
-    run_cbindgen(&cargo_dir, &out_dir);
+    run_cbindgen(&cargo_dir, &target_dir);
     run_bindgen(&target, &out_dir);
 }
 
-fn run_cbindgen(_cargo_dir: &Path, _out_dir: &Path) {
-    // TODO: Run cbindgen
+fn run_cbindgen(cargo_dir: &Path, target_dir: &Path) {
+    let out = target_dir.join("RustApi.h");
+
+    cbindgen::Builder::new()
+        .with_crate(cargo_dir)
+        .with_language(cbindgen::Language::C)
+        .generate()
+        .expect("Unable to generate bindings")
+        .write_to_file(&out);
+
+    println!("cargo:rerun-if-changed={}", out.display());
 }
 
 fn run_bindgen(target: &str, out_dir: &Path) {
+    let header = "../clib/include/CApi.h";
+    let out = out_dir.join("bindings.rs");
+
     let mut builder = bindgen::Builder::default();
-    builder = builder.header("../main/CApi.h");
+    builder = builder.header(header);
     match target {
         "riscv32i-unknown-none-elf" => {
             builder = builder.clang_arg("--target=riscv32");
@@ -36,6 +49,9 @@ fn run_bindgen(target: &str, out_dir: &Path) {
 
     let bindings = builder.generate().expect("Couldn't generate bindings!");
     bindings
-        .write_to_file(out_dir.join("bindings.rs"))
+        .write_to_file(&out)
         .expect("Couldn't save bindings!");
+
+    println!("cargo:rerun-if-changed={}", header);
+    println!("cargo:rerun-if-changed={}", out.display());
 }

components/rustlib/placeholder.c

@@ -0,0 +1,13 @@
+/* Hello World Example
+
+   This example code is in the Public Domain (or CC0 licensed, at your option.)
+
+   Unless required by applicable law or agreed to in writing, this
+   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+   CONDITIONS OF ANY KIND, either express or implied.
+*/
+
+/* This is an empty source file to force the build of a CMake library that
+   can participate in the CMake dependency graph. This placeholder library
+   will depend on the actual library generated by external Rust build.
+*/

components/rustlib/src/lib.rs

@@ -26,7 +26,7 @@ pub mod sys {
 pub extern "C" fn add_in_rust(x: i32, y: i32) -> i32 {
     unsafe {
         sys::validate_param_in_c(0, x);
-        sys::validate_param_in_c(2, y);
+        sys::validate_param_in_c(1, y);
     }
     x + y
 }

main/CMakeLists.txt

@@ -1,46 +1,2 @@
 idf_component_register(SRCS "main.c"
                     INCLUDE_DIRS "")
-
-set(CARGO_BUILD_TYPE "release")
-set(CARGO_BUILD_ARG "--release")
-if(CONFIG_IDF_TARGET_ARCH_RISCV)
-    set(CARGO_TARGET "riscv32i-unknown-none-elf")
-    set(CARGO_FEATURES_ARG "")
-elseif(CONFIG_IDF_TARGET_ARCH_XTENSA)
-    set(CARGO_TARGET "xtensa-esp32-none-elf")
-    set(CARGO_FEATURES_ARG "--features=std")
-endif()
-
-set(RUST_PROJECT_DIR "${CMAKE_CURRENT_LIST_DIR}/../rustlib")
-set(RUST_BUILD_DIR "${CMAKE_CURRENT_BINARY_DIR}/rustlib")
-set(RUST_STATIC_LIBRARY "${RUST_BUILD_DIR}/${CARGO_TARGET}/${CARGO_BUILD_TYPE}/librustlib.a")
-
-ExternalProject_Add(
-    rustlib_project
-    PREFIX "${RUST_PROJECT_DIR}"
-    BUILD_COMMAND ${CMAKE_COMMAND} -E env
-        CARGO_BUILD_TARGET=${CARGO_TARGET}
-        CARGO_BUILD_TARGET_DIR=${RUST_BUILD_DIR}
-        cargo build ${CARGO_BUILD_ARG} ${CARGO_FEATURES_ARG}
-    DOWNLOAD_COMMAND ""
-    CONFIGURE_COMMAND ""
-    INSTALL_COMMAND ""
-    BUILD_ALWAYS TRUE
-    BUILD_DIR "${RUST_BUILD_DIR}"
-    INSTALL_DIR "${RUST_BUILD_DIR}"
-    STAMP_DIR "${RUST_BUILD_DIR}/stamp"
-    TMP_DIR "${RUST_BUILD_DIR}/tmp"
-    DOWNLOAD_DIR "${RUST_BUILD_DIR}"
-    SOURCE_DIR "${RUST_PROJECT_DIR}"
-    BUILD_BYPRODUCTS "${RUST_STATIC_LIBRARY}"
-)
-
-# this adds "rustlib" static library target.
-# PRIV_REQUIRES tells CMake that librustlib.a itself depends on libmain.a.
-add_prebuilt_library(rustlib "${RUST_STATIC_LIBRARY}" PRIV_REQUIRES main)
-
-# rustlib will be produced by building rustlib_project target
-add_dependencies(rustlib rustlib_project)
-
-# 'main' calls a function from the library, so link it to 'main'
-target_link_libraries(${COMPONENT_LIB} PRIVATE rustlib)

main/RustApi.h

@@ -1,5 +0,0 @@
-/* 
- * Rust functions exposed to C.
- */
-
-extern int add_in_rust(int x, int y);

main/component.mk

@@ -1,5 +0,0 @@
-#
-# "main" pseudo-component makefile.
-#
-# (Uses default behaviour of compiling all source files in directory, adding 'include' to include path.)
-

main/main.c

@@ -13,7 +13,6 @@
 #include "esp_system.h"
 #include "esp_spi_flash.h"
 
-#include "CApi.h"
 #include "RustApi.h"
 
 void app_main(void)
@@ -49,16 +48,3 @@ void app_main(void)
     fflush(stdout);
     esp_restart();
 }
-
-// bool validate_param_in_c(const char *param, int value)
-// {
-//     printf("C validated %s = %d\n", param, value);
-//     return true;
-// }
-
-
-bool validate_param_in_c(int param, int value)
-{
-    printf("C validated %d = %d\n", param, value);
-    return true;
-}

rustlib/cbindgen.toml

@@ -1 +0,0 @@
-language = "C"