ot/earlgrey-cw310: support alternative linker script for tests

This commit fixes the hack where OT currently relies on overwriting the
linker script in the target directory, instead using a custom build.rs
to allow this board to override the linker script in use based on the
value of an environment variable. This PR also includes
some cleanup to remove some lines that I believe are no longer necessary
in the current build system. These line were scattered around the "test"
rule for various boards and would directly copy files into the build
directory, but I that is already handled by Cargo today.

boards/apollo3/lora_things_plus/Makefile

@@ -44,10 +44,8 @@ flash-app:
 
 .PHONY: test
 test:
-	mkdir -p $(TOCK_ROOT_DIRECTORY)target/$(TARGET)/release/deps/
 	$(Q)OBJCOPY=${OBJCOPY} PORT=$(PORT) $(CARGO) test $(NO_RUN) --bin $(PLATFORM) --release
 
 .PHONY: test-atecc508a
 test-atecc508a:
-	mkdir -p $(TOCK_ROOT_DIRECTORY)target/$(TARGET)/release/deps/
 	$(Q)OBJCOPY=${OBJCOPY} PORT=$(PORT) $(CARGO) test $(NO_RUN) --bin $(PLATFORM) --release --features atecc508a

boards/apollo3/redboard_artemis_atp/Makefile

@@ -44,5 +44,4 @@ flash-app:
 
 .PHONY: test
 test:
-	mkdir -p $(TOCK_ROOT_DIRECTORY)target/$(TARGET)/release/deps/
 	$(Q)OBJCOPY=${OBJCOPY} PORT=$(PORT) $(CARGO) test $(NO_RUN) --bin $(PLATFORM) --release

boards/apollo3/redboard_artemis_nano/Makefile

@@ -44,5 +44,4 @@ flash-app:
 
 .PHONY: test
 test:
-	mkdir -p $(TOCK_ROOT_DIRECTORY)target/$(TARGET)/release/deps/
 	$(Q)OBJCOPY=${OBJCOPY} PORT=$(PORT) $(CARGO) test $(NO_RUN) --bin $(PLATFORM) --release

boards/build_scripts/src/default.rs

@@ -25,6 +25,43 @@ pub fn default_linker_script() {
         panic!("Boards must provide a `layout.ld` link script file");
     }
 
+    rustflags_check();
+
+    include_tock_kernel_layout();
+
+    add_board_dir_to_linker_search_path();
+
+    set_and_track_linker_script(LINKER_SCRIPT);
+}
+
+/// Include the folder where the board's Cargo.toml is in the linker file
+/// search path.
+pub fn add_board_dir_to_linker_search_path() {
+    // Note this is a different path than the one returned by
+    // `std::env!("CARGO_MANIFEST_DIR")` in `include_tock_kernel_layout()`,
+    // since that is evaluated at compile
+    // time while this `std::env::var("CARGO_MANIFEST_DIR")` is evaluated at runtime.
+    println!(
+        "cargo:rustc-link-arg=-L{}",
+        std::env::var("CARGO_MANIFEST_DIR").unwrap()
+    );
+}
+
+/// Include the folder where this build_script crate's Cargo.toml is in the
+/// linker file search path for `tock_kernel_layout.ld`, and instruct cargo
+/// to rebuild if that linker script is changed.
+pub fn include_tock_kernel_layout() {
+    println!("cargo:rustc-link-arg=-L{}", std::env!("CARGO_MANIFEST_DIR"));
+    // Directive to rebuild if the linker script in this crate is changed.
+    println!(
+        "cargo:rerun-if-changed={}",
+        Path::new(std::env!("CARGO_MANIFEST_DIR"))
+            .join("tock_kernel_layout.ld")
+            .to_string_lossy()
+    );
+}
+
+pub fn rustflags_check() {
     // The `RUSTFLAGS` that the Tock config files set can be easily overridden
     // by command line flags. The build will still succeed but the resulting
     // binary may be invalid as it was not built with the intended flags. This
@@ -50,33 +87,18 @@ pub fn default_linker_script() {
             );
         }
     }
+}
 
-    // Include the folder where this build_script crate's Cargo.toml is in the
-    // linker file search path for `tock_kernel_layout.ld`.
-    println!("cargo:rustc-link-arg=-L{}", std::env!("CARGO_MANIFEST_DIR"));
-    // Directive to rebuild if the linker script in this crate is changed.
-    println!(
-        "cargo:rerun-if-changed={}",
-        Path::new(std::env!("CARGO_MANIFEST_DIR"))
-            .join("tock_kernel_layout.ld")
-            .to_string_lossy()
-    );
-
-    // Include the folder where the board's Cargo.toml is in the linker file
-    // search path.
-    println!(
-        "cargo:rustc-link-arg=-L{}",
-        std::env::var("CARGO_MANIFEST_DIR").unwrap()
-    );
-    // `-Tlayout.ld`: Use the linker script `layout.ld` all boards must provide.
-    println!("cargo:rustc-link-arg=-T{}", LINKER_SCRIPT);
-
-    track_linker_script(LINKER_SCRIPT);
+/// Pass the given linker script to cargo, and track it and all of its `INCLUDE`s
+pub fn set_and_track_linker_script<P: AsRef<Path> + ToString>(path: P) {
+    // Use the passed linker script
+    println!("cargo:rustc-link-arg=-T{}", path.to_string());
+    track_linker_script(path);
 }
 
 /// Track the given linker script and all of its `INCLUDE`s so that the build
 /// is rerun when any of them change.
-fn track_linker_script<P: AsRef<Path>>(path: P) {
+pub fn track_linker_script<P: AsRef<Path>>(path: P) {
     let path = path.as_ref();
 
     // Skip the default Tock linker script as we have manually added the

boards/build_scripts/src/lib.rs

@@ -2,6 +2,6 @@
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 // Copyright Tock Contributors 2024.
 
-mod default;
+pub mod default;
 
 pub use default::default_linker_script;

boards/esp32-c3-devkitM-1/Makefile

@@ -25,5 +25,4 @@ endif
 	esptool.py --port /dev/ttyUSB0 --chip esp32c3 write_flash --flash_mode dio --flash_size detect --flash_freq 80m 0x0 binary.hex
 
 test:
-	mkdir -p $(TOCK_ROOT_DIRECTORY)target/$(TARGET)/release/deps/
 	$(Q)$(CARGO) test $(NO_RUN) --bin $(PLATFORM) --release

boards/opentitan/earlgrey-cw310/Cargo.toml

@@ -6,7 +6,7 @@
 name = "earlgrey-cw310"
 version.workspace = true
 authors.workspace = true
-build = "../../build.rs"
+build = "build.rs"
 edition.workspace = true
 
 [dependencies]

boards/opentitan/earlgrey-cw310/Makefile

@@ -108,16 +108,10 @@ test:
 ifneq ($(OPENTITAN_TREE),)
 	$(error "Running on QEMU, use test-hardware to run on hardware")
 endif
-	mkdir -p $(TOCK_ROOT_DIRECTORY)target/$(TARGET)/release/deps/
-	$(Q)cp test_layout.ld $(TOCK_ROOT_DIRECTORY)target/$(TARGET)/release/deps/layout.ld
-	$(Q)TOCK_ROOT_DIRECTORY=${TOCK_ROOT_DIRECTORY} QEMU_ENTRY_POINT=${QEMU_ENTRY_POINT} TARGET=${TARGET} $(CARGO) test $(CARGO_FLAGS) $(NO_RUN) --bin $(PLATFORM) --release
+	$(Q)TOCK_ROOT_DIRECTORY=${TOCK_ROOT_DIRECTORY} QEMU_ENTRY_POINT=${QEMU_ENTRY_POINT} TARGET=${TARGET} LINKER_SCRIPT_OVERRIDE=test_layout.ld $(CARGO) test $(CARGO_FLAGS) $(NO_RUN) --bin $(PLATFORM) --release
 
 test-hardware: ot-check
-	mkdir -p $(TOCK_ROOT_DIRECTORY)target/$(TARGET)/release/deps/
-	$(Q)cp test_layout.ld $(TOCK_ROOT_DIRECTORY)target/$(TARGET)/release/deps/layout.ld
-	$(Q)OBJCOPY=$(RISC_PREFIX)-objcopy TOCK_ROOT_DIRECTORY=${TOCK_ROOT_DIRECTORY} TARGET=${TARGET} $(CARGO) test $(CARGO_FLAGS) $(NO_RUN) --bin $(PLATFORM) --release --features=hardware_tests
+	$(Q)OBJCOPY=$(RISC_PREFIX)-objcopy TOCK_ROOT_DIRECTORY=${TOCK_ROOT_DIRECTORY} TARGET=${TARGET} LINKER_SCRIPT_OVERRIDE=test_layout.ld $(CARGO) test $(CARGO_FLAGS) $(NO_RUN) --bin $(PLATFORM) --release --features=hardware_tests
 
 test-verilator: ot-check
-	mkdir -p $(TOCK_ROOT_DIRECTORY)target/$(TARGET)/release/deps/
-	$(Q)cp test_layout.ld $(TOCK_ROOT_DIRECTORY)target/$(TARGET)/release/deps/layout.ld
-	$(Q)VERILATOR="yes" OBJCOPY=$(RISC_PREFIX)-objcopy TOCK_ROOT_DIRECTORY=${TOCK_ROOT_DIRECTORY} TARGET=${TARGET} $(CARGO) test $(CARGO_FLAGS) $(NO_RUN) --bin $(PLATFORM) --release --features=hardware_tests,sim_verilator
+	$(Q)VERILATOR="yes" OBJCOPY=$(RISC_PREFIX)-objcopy TOCK_ROOT_DIRECTORY=${TOCK_ROOT_DIRECTORY} TARGET=${TARGET} LINKER_SCRIPT_OVERRIDE=test_layout.ld $(CARGO) test $(CARGO_FLAGS) $(NO_RUN) --bin $(PLATFORM) --release --features=hardware_tests,sim_verilator

boards/opentitan/earlgrey-cw310/build.rs

@@ -0,0 +1,29 @@
+// Licensed under the Apache License, Version 2.0 or the MIT License.
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+// Copyright Tock Contributors 2024.
+
+//! This board uses a custom build script to enable selecting a different layout
+//! file for tests, which require a different layout than normal kernel builds.
+//! The script is lightly adapted from the `default_linker_script` in
+//! `tock_build_scripts`, and uses the functions provided by that crate.
+
+use std::path::Path;
+
+const LINKER_SCRIPT_OVERRIDE_ENV: &str = "LINKER_SCRIPT_OVERRIDE";
+
+fn main() {
+    let linker_script =
+        std::env::var(LINKER_SCRIPT_OVERRIDE_ENV).unwrap_or("layout.ld".to_string());
+    println!("cargo:rerun-if-env-changed={}", LINKER_SCRIPT_OVERRIDE_ENV);
+
+    if !Path::new(&linker_script).exists() {
+        panic!(
+            "Boards must provide a linker script file; path does not exist: {:?}",
+            linker_script
+        );
+    }
+    tock_build_scripts::default::rustflags_check();
+    tock_build_scripts::default::include_tock_kernel_layout();
+    tock_build_scripts::default::add_board_dir_to_linker_search_path();
+    tock_build_scripts::default::set_and_track_linker_script(linker_script);
+}

boards/opentitan/earlgrey-cw310/run.sh

@@ -6,9 +6,6 @@
 
 BUILD_DIR="verilator_build/"
 
-# Preemptively cleanup layout (incase this was a test) so that following apps (non-tests) load the correct layout.
-rm $TOCK_ROOT_DIRECTORY/target/$TARGET/release/deps/layout.ld
-
 if [[ "${VERILATOR}" == "yes" ]]; then
 		if [ -d "$BUILD_DIR" ]; then
 			# Cleanup before we build again