Fixes #177 -- let the kernel build process drive cargo

Author: alex

.gitignore

@@ -9,3 +9,4 @@ Module.symvers
 *.mod.c
 *.o
 modules.order
+dummy.c

README.md

@@ -57,7 +57,8 @@ environment variable appropriately, e.g., `CLANG=clang-9`.
 
 ## Building hello-world
 
-1. Install clang, kernel headers, and the `rust-src` and `rustfmt` components from `rustup`:
+1. Install clang, kernel headers, and the `rust-src` and `rustfmt` components
+from `rustup`:
 
 ```
 apt-get install llvm clang linux-headers-"$(uname -r)" # or the equivalent for your OS
@@ -70,19 +71,14 @@ rustup component add --toolchain=nightly rust-src rustfmt
 cd hello-world
 ```
 
-3. Build the static object with cargo build, cross-compiling for the kernel target
-
-```
-cargo build -Z build-std=core,alloc --target x86_64-linux-kernel
-```
-
-4. Build the kernel module using the Linux kernel build system (kbuild)
+3. Build the kernel module using the Linux kernel build system (kbuild), this
+will invoke `cargo` to build the Rust code
 
 ```
 make
 ```
 
-5. Load and unload the module!
+4. Load and unload the module!
 
 ```
 sudo insmod helloworld.ko

build.rs

@@ -98,6 +98,12 @@ fn handle_kernel_symbols_cfg(symvers_path: &PathBuf) {
     }
 }
 
+fn add_env_if_present(cmd: &mut Command, var: &str) {
+    if let Ok(val) = env::var(var) {
+        cmd.env(var, val);
+    }
+}
+
 fn main() {
     println!("cargo:rerun-if-env-changed=KDIR");
     let kdir = env::var("KDIR").unwrap_or(format!(
@@ -109,12 +115,15 @@ fn main() {
 
     println!("cargo:rerun-if-env-changed=CLANG");
     println!("cargo:rerun-if-changed=kernel-cflags-finder/Makefile");
-    let output = Command::new("make")
-        .arg("-C")
+    let mut cmd = Command::new("make");
+    cmd.arg("-C")
         .arg("kernel-cflags-finder")
         .arg("-s")
-        .output()
-        .unwrap();
+        .env_clear();
+    add_env_if_present(&mut cmd, "KDIR");
+    add_env_if_present(&mut cmd, "CLANG");
+    add_env_if_present(&mut cmd, "PATH");
+    let output = cmd.output().unwrap();
     if !output.status.success() {
         eprintln!("kernel-cflags-finder did not succeed");
         eprintln!("stdout: {}", std::str::from_utf8(&output.stdout).unwrap());
@@ -161,7 +170,6 @@ fn main() {
     handle_kernel_symbols_cfg(&PathBuf::from(&kdir).join("Module.symvers"));
 
     let mut builder = cc::Build::new();
-    println!("cargo:rerun-if-env-changed=CLANG");
     builder.compiler(env::var("CLANG").unwrap_or("clang".to_string()));
     builder.target(&target);
     builder.warnings(false);

hello-world/Makefile

@@ -1,12 +1,19 @@
+ifneq ($(KERNELRELEASE),)
 obj-m := helloworld.o
 helloworld-objs := hello_world.rust.o
-KDIR ?= /lib/modules/$(shell uname -r)/build
+
+$(src)/target/x86_64-linux-kernel/debug/libhello_world.a: $(src)/Cargo.toml $(wildcard $(src)/src/*.c)
+	cd $(src); env -u MAKE -u MAKEFLAGS cargo build -Z build-std=core,alloc --target=x86_64-linux-kernel
 
 %.rust.o: target/x86_64-linux-kernel/debug/lib%.a
 	$(LD) -r -o $@ --whole-archive $<
 
+else
+KDIR ?= /lib/modules/$(shell uname -r)/build
+
 all:
 	$(MAKE) -C $(KDIR) M=$(CURDIR)
 
 clean:
 	$(MAKE) -C $(KDIR) M=$(CURDIR) clean
+endif

kernel-cflags-finder/.gitignore

@@ -5,7 +5,6 @@
 .tmp_versions/
 Module.symvers
 built-in.o
-dummy.c
 dummy.ko
 dummy.mod.c
 dummy.mod.o

tests/Makefile

@@ -1,12 +1,19 @@
+ifneq ($(KERNELRELEASE),)
 obj-m := testmodule.o
 testmodule-objs := $(TEST_NAME).rust.o
-KDIR ?= /lib/modules/$(shell uname -r)/build
+
+$(src)/target/x86_64-linux-kernel/debug/lib%.a: $(src)/$(TEST_PATH)/Cargo.toml $(wildcard $(src)/$(TEST_PATH)/src/*.rs)
+	cd $(src)/$(TEST_PATH); env -u MAKE -u MAKEFLAGS RUSTFLAGS="-Dwarnings" CARGO_TARGET_DIR=../target cargo build -Z build-std=core,alloc --target=x86_64-linux-kernel
 
 %.rust.o: target/x86_64-linux-kernel/debug/lib%.a
 	$(LD) -r -o $@ --whole-archive $<
 
+else
+KDIR ?= /lib/modules/$(shell uname -r)/build
+
 all:
 	$(MAKE) -C $(KDIR) M=$(CURDIR)
 
 clean:
 	$(MAKE) -C $(KDIR) M=$(CURDIR) clean
+endif

tests/run_tests.py

@@ -27,23 +27,11 @@ def main(argv):
             continue
 
         print("+ [{}]".format(path))
-        run(
-            "cargo", "build", "-Zbuild-std=core,alloc",
-            "--target", target,
-            cwd=os.path.join(BASE_DIR, path),
-            environ=dict(
-                os.environ,
-                RUSTFLAGS="-Dwarnings",
-                CARGO_TARGET_DIR=os.path.relpath(
-                    os.path.join(BASE_DIR, "target"),
-                    os.path.join(BASE_DIR, path)
-                ),
-            )
-        )
 
         run(
             "make", "-C", BASE_DIR,
             "TEST_NAME={}_tests".format(path.replace("-", "_")),
+            "TEST_PATH={}".format(path),
         )
         # TODO: qemu
         run(