Initial support for building RISC-V runtimes targeting PolkaVM (#3179)

This PR adds initial support for building RISC-V runtimes targeting
PolkaVM.

- Setting the `SUBSTRATE_RUNTIME_TARGET=riscv` environment variable will
now build a RISC-V runtime instead of a WASM runtime.
- This only adds support for *building* runtimes; running them will need
a PolkaVM-based executor, which I will add in a future PR.
- Only building the minimal runtime is supported (building the Polkadot
runtime doesn't work *yet* due to one of the dependencies).
- The builder now sets a `substrate_runtime` cfg flag when building the
runtimes, with the idea being that instead of doing `#[cfg(not(feature =
"std"))]` or `#[cfg(target_arch = "wasm32")]` to detect that we're
building a runtime you'll do `#[cfg(substrate_runtime)]`. (Switching the
whole codebase to use this will be done in a future PR; I deliberately
didn't do this here to keep this PR minimal and reviewable.)
- Further renaming of things (e.g. types, environment variables and proc
macro attributes having "wasm" in their name) to be target-agnostic will
also be done in a future refactoring PR (while keeping backwards
compatibility where it makes sense; I don't intend to break anyone's
workflow or create unnecessary churn).
- This PR also fixes two bugs in the `wasm-builder` crate:
* The `RUSTC` environment variable is now removed when invoking the
compiler. This prevents the toolchain version from being overridden when
called from a `build.rs` script.
* When parsing the `rustup toolchain list` output the `(default)` is now
properly stripped and not treated as part of the version.
- I've also added a minimal CI job that makes sure this doesn't break in
the future. (cc @paritytech/ci)

cc @athei

------

Also, just a fun little tidbit: quickly comparing the size of the built
runtimes it seems that the PolkaVM runtime is slightly smaller than the
WASM one. (`production` build, with the `names` section substracted from
the WASM's size to keep things fair, since for the PolkaVM runtime we're
currently stripping out everything)

- `.wasm`: 625505 bytes
- `.wasm` (after wasm-opt -O3): 563205 bytes
- `.wasm` (after wasm-opt -Os): 562987 bytes
- `.wasm` (after wasm-opt -Oz): 536852 bytes
- `.polkavm`: ~~580338 bytes~~ 550476 bytes (after enabling extra target
features; I'll add those in another PR once we have an executor working)

---------

Co-authored-by: Bastian Köcher <git@kchr.de>

substrate/utils/wasm-builder/src/builder.rs

@@ -21,6 +21,8 @@ use std::{
 	process,
 };
 
+use crate::RuntimeTarget;
+
 /// Returns the manifest dir from the `CARGO_MANIFEST_DIR` env.
 fn get_manifest_dir() -> PathBuf {
 	env::var("CARGO_MANIFEST_DIR")
@@ -49,6 +51,8 @@ impl WasmBuilderSelectProject {
 			project_cargo_toml: get_manifest_dir().join("Cargo.toml"),
 			features_to_enable: Vec::new(),
 			disable_runtime_version_section_check: false,
+			export_heap_base: false,
+			import_memory: false,
 		}
 	}
 
@@ -65,6 +69,8 @@ impl WasmBuilderSelectProject {
 				project_cargo_toml: path,
 				features_to_enable: Vec::new(),
 				disable_runtime_version_section_check: false,
+				export_heap_base: false,
+				import_memory: false,
 			})
 		} else {
 			Err("Project path must point to the `Cargo.toml` of the project")
@@ -97,6 +103,11 @@ pub struct WasmBuilder {
 	features_to_enable: Vec<String>,
 	/// Should the builder not check that the `runtime_version` section exists in the wasm binary?
 	disable_runtime_version_section_check: bool,
+
+	/// Whether `__heap_base` should be exported (WASM-only).
+	export_heap_base: bool,
+	/// Whether `--import-memory` should be added to the link args (WASM-only).
+	import_memory: bool,
 }
 
 impl WasmBuilder {
@@ -109,7 +120,7 @@ impl WasmBuilder {
 	///
 	/// This adds `-Clink-arg=--export=__heap_base` to `RUST_FLAGS`.
 	pub fn export_heap_base(mut self) -> Self {
-		self.rust_flags.push("-Clink-arg=--export=__heap_base".into());
+		self.export_heap_base = true;
 		self
 	}
 
@@ -127,7 +138,7 @@ impl WasmBuilder {
 	///
 	/// This adds `-C link-arg=--import-memory` to `RUST_FLAGS`.
 	pub fn import_memory(mut self) -> Self {
-		self.rust_flags.push("-C link-arg=--import-memory".into());
+		self.import_memory = true;
 		self
 	}
 
@@ -159,7 +170,18 @@ impl WasmBuilder {
 	}
 
 	/// Build the WASM binary.
-	pub fn build(self) {
+	pub fn build(mut self) {
+		let target = crate::runtime_target();
+		if target == RuntimeTarget::Wasm {
+			if self.export_heap_base {
+				self.rust_flags.push("-Clink-arg=--export=__heap_base".into());
+			}
+
+			if self.import_memory {
+				self.rust_flags.push("-C link-arg=--import-memory".into());
+			}
+		}
+
 		let out_dir = PathBuf::from(env::var("OUT_DIR").expect("`OUT_DIR` is set by cargo!"));
 		let file_path =
 			out_dir.join(self.file_name.clone().unwrap_or_else(|| "wasm_binary.rs".into()));
@@ -175,6 +197,7 @@ impl WasmBuilder {
 		}
 
 		build_project(
+			target,
 			file_path,
 			self.project_cargo_toml,
 			self.rust_flags.into_iter().map(|f| format!("{} ", f)).collect(),
@@ -248,6 +271,7 @@ fn generate_rerun_if_changed_instructions() {
 /// `check_for_runtime_version_section` - Should the wasm binary be checked for the
 /// `runtime_version` section?
 fn build_project(
+	target: RuntimeTarget,
 	file_name: PathBuf,
 	project_cargo_toml: PathBuf,
 	default_rustflags: String,
@@ -255,7 +279,7 @@ fn build_project(
 	wasm_binary_name: Option<String>,
 	check_for_runtime_version_section: bool,
 ) {
-	let cargo_cmd = match crate::prerequisites::check() {
+	let cargo_cmd = match crate::prerequisites::check(target) {
 		Ok(cmd) => cmd,
 		Err(err_msg) => {
 			eprintln!("{}", err_msg);
@@ -264,6 +288,7 @@ fn build_project(
 	};
 
 	let (wasm_binary, bloaty) = crate::wasm_project::create_and_compile(
+		target,
 		&project_cargo_toml,
 		&default_rustflags,
 		cargo_cmd,

substrate/utils/wasm-builder/src/lib.rs

@@ -113,6 +113,7 @@
 //! wasm32-unknown-unknown --toolchain nightly-2020-02-20`.
 
 use std::{
+	collections::BTreeSet,
 	env, fs,
 	io::BufRead,
 	path::{Path, PathBuf},
@@ -164,6 +165,9 @@ const WASM_BUILD_WORKSPACE_HINT: &str = "WASM_BUILD_WORKSPACE_HINT";
 /// Environment variable to set whether we'll build `core`/`std`.
 const WASM_BUILD_STD: &str = "WASM_BUILD_STD";
 
+/// The target to use for the runtime. Valid values are `wasm` (default) or `riscv`.
+const RUNTIME_TARGET: &str = "SUBSTRATE_RUNTIME_TARGET";
+
 /// Write to the given `file` if the `content` is different.
 fn write_file_if_changed(file: impl AsRef<Path>, content: impl AsRef<str>) {
 	if fs::read_to_string(file.as_ref()).ok().as_deref() != Some(content.as_ref()) {
@@ -185,7 +189,7 @@ fn copy_file_if_changed(src: PathBuf, dst: PathBuf) {
 }
 
 /// Get a cargo command that should be used to invoke the compilation.
-fn get_cargo_command() -> CargoCommand {
+fn get_cargo_command(target: RuntimeTarget) -> CargoCommand {
 	let env_cargo =
 		CargoCommand::new(&env::var("CARGO").expect("`CARGO` env variable is always set by cargo"));
 	let default_cargo = CargoCommand::new("cargo");
@@ -196,35 +200,33 @@ fn get_cargo_command() -> CargoCommand {
 		wasm_toolchain.map(|t| CargoCommand::new_with_args("rustup", &["run", &t, "cargo"]))
 	{
 		cmd
-	} else if env_cargo.supports_substrate_wasm_env() {
+	} else if env_cargo.supports_substrate_runtime_env(target) {
 		env_cargo
-	} else if default_cargo.supports_substrate_wasm_env() {
+	} else if default_cargo.supports_substrate_runtime_env(target) {
 		default_cargo
 	} else {
 		// If no command before provided us with a cargo that supports our Substrate wasm env, we
 		// try to search one with rustup. If that fails as well, we return the default cargo and let
 		// the prequisities check fail.
-		get_rustup_command().unwrap_or(default_cargo)
+		get_rustup_command(target).unwrap_or(default_cargo)
 	}
 }
 
-/// Get the newest rustup command that supports our Substrate wasm env.
+/// Get the newest rustup command that supports compiling a runtime.
 ///
 /// Stable versions are always favored over nightly versions even if the nightly versions are
 /// newer.
-fn get_rustup_command() -> Option<CargoCommand> {
-	let host = format!("-{}", env::var("HOST").expect("`HOST` is always set by cargo"));
-
+fn get_rustup_command(target: RuntimeTarget) -> Option<CargoCommand> {
 	let output = Command::new("rustup").args(&["toolchain", "list"]).output().ok()?.stdout;
 	let lines = output.as_slice().lines();
 
 	let mut versions = Vec::new();
 	for line in lines.filter_map(|l| l.ok()) {
-		let rustup_version = line.trim_end_matches(&host);
-
+		// Split by a space to get rid of e.g. " (default)" at the end.
+		let rustup_version = line.split(" ").next().unwrap();
 		let cmd = CargoCommand::new_with_args("rustup", &["run", &rustup_version, "cargo"]);
 
-		if !cmd.supports_substrate_wasm_env() {
+		if !cmd.supports_substrate_runtime_env(target) {
 			continue
 		}
 
@@ -247,22 +249,26 @@ struct CargoCommand {
 	program: String,
 	args: Vec<String>,
 	version: Option<Version>,
+	target_list: Option<BTreeSet<String>>,
 }
 
 impl CargoCommand {
 	fn new(program: &str) -> Self {
 		let version = Self::extract_version(program, &[]);
+		let target_list = Self::extract_target_list(program, &[]);
 
-		CargoCommand { program: program.into(), args: Vec::new(), version }
+		CargoCommand { program: program.into(), args: Vec::new(), version, target_list }
 	}
 
 	fn new_with_args(program: &str, args: &[&str]) -> Self {
 		let version = Self::extract_version(program, args);
+		let target_list = Self::extract_target_list(program, args);
 
 		CargoCommand {
 			program: program.into(),
 			args: args.iter().map(ToString::to_string).collect(),
 			version,
+			target_list,
 		}
 	}
 
@@ -283,6 +289,23 @@ impl CargoCommand {
 		Version::extract(&version)
 	}
 
+	fn extract_target_list(program: &str, args: &[&str]) -> Option<BTreeSet<String>> {
+		// This is technically an unstable option, but we don't care because we only need this
+		// to build RISC-V runtimes, and those currently require a specific nightly toolchain
+		// anyway, so it's totally fine for this to fail in other cases.
+		let list = Command::new(program)
+			.args(args)
+			.args(&["rustc", "-Z", "unstable-options", "--print", "target-list"])
+			// Make sure if we're called from within a `build.rs` the host toolchain won't override
+			// a rustup toolchain we've picked.
+			.env_remove("RUSTC")
+			.output()
+			.ok()
+			.and_then(|o| String::from_utf8(o.stdout).ok())?;
+
+		Some(list.trim().split("\n").map(ToString::to_string).collect())
+	}
+
 	/// Returns the version of this cargo command or `None` if it failed to extract the version.
 	fn version(&self) -> Option<Version> {
 		self.version
@@ -294,12 +317,29 @@ impl CargoCommand {
 			env::var("RUSTC_BOOTSTRAP").is_ok()
 	}
 
+	/// Check if the supplied cargo command supports our runtime environment.
+	fn supports_substrate_runtime_env(&self, target: RuntimeTarget) -> bool {
+		match target {
+			RuntimeTarget::Wasm => self.supports_substrate_runtime_env_wasm(),
+			RuntimeTarget::Riscv => self.supports_substrate_runtime_env_riscv(),
+		}
+	}
+
+	/// Check if the supplied cargo command supports our RISC-V runtime environment.
+	fn supports_substrate_runtime_env_riscv(&self) -> bool {
+		let Some(target_list) = self.target_list.as_ref() else { return false };
+		// This is our custom target which currently doesn't exist on any upstream toolchain,
+		// so if it exists it's guaranteed to be our custom toolchain and have have everything
+		// we need, so any further version checks are unnecessary at this point.
+		target_list.contains("riscv32ema-unknown-none-elf")
+	}
+
 	/// Check if the supplied cargo command supports our Substrate wasm environment.
 	///
 	/// This means that either the cargo version is at minimum 1.68.0 or this is a nightly cargo.
 	///
 	/// Assumes that cargo version matches the rustc version.
-	fn supports_substrate_wasm_env(&self) -> bool {
+	fn supports_substrate_runtime_env_wasm(&self) -> bool {
 		// `RUSTC_BOOTSTRAP` tells a stable compiler to behave like a nightly. So, when this env
 		// variable is set, we can assume that whatever rust compiler we have, it is a nightly
 		// compiler. For "more" information, see:
@@ -365,5 +405,48 @@ fn get_bool_environment_variable(name: &str) -> Option<bool> {
 
 /// Returns whether we need to also compile the standard library when compiling the runtime.
 fn build_std_required() -> bool {
-	crate::get_bool_environment_variable(crate::WASM_BUILD_STD).unwrap_or(true)
+	let default = runtime_target() == RuntimeTarget::Wasm;
+
+	crate::get_bool_environment_variable(crate::WASM_BUILD_STD).unwrap_or(default)
+}
+
+#[derive(Copy, Clone, PartialEq, Eq)]
+enum RuntimeTarget {
+	Wasm,
+	Riscv,
+}
+
+impl RuntimeTarget {
+	fn rustc_target(self) -> &'static str {
+		match self {
+			RuntimeTarget::Wasm => "wasm32-unknown-unknown",
+			RuntimeTarget::Riscv => "riscv32ema-unknown-none-elf",
+		}
+	}
+
+	fn build_subdirectory(self) -> &'static str {
+		// Keep the build directories separate so that when switching between
+		// the targets we won't trigger unnecessary rebuilds.
+		match self {
+			RuntimeTarget::Wasm => "wbuild",
+			RuntimeTarget::Riscv => "rbuild",
+		}
+	}
+}
+
+fn runtime_target() -> RuntimeTarget {
+	let Some(value) = env::var_os(RUNTIME_TARGET) else {
+		return RuntimeTarget::Wasm;
+	};
+
+	if value == "wasm" {
+		RuntimeTarget::Wasm
+	} else if value == "riscv" {
+		RuntimeTarget::Riscv
+	} else {
+		build_helper::warning!(
+			"the '{RUNTIME_TARGET}' environment variable has an invalid value; it must be either 'wasm' or 'riscv'"
+		);
+		std::process::exit(1);
+	}
 }

substrate/utils/wasm-builder/src/prerequisites.rs

@@ -15,14 +15,19 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use crate::{write_file_if_changed, CargoCommand, CargoCommandVersioned};
+use crate::{write_file_if_changed, CargoCommand, CargoCommandVersioned, RuntimeTarget};
 
 use console::style;
-use std::{fs, path::Path};
+use std::{
+	fs,
+	path::{Path, PathBuf},
+	process::Command,
+};
+
 use tempfile::tempdir;
 
-/// Print an error message.
-fn print_error_message(message: &str) -> String {
+/// Colorizes an error message, if color output is enabled.
+fn colorize_error_message(message: &str) -> String {
 	if super::color_output_enabled() {
 		style(message).red().bold().to_string()
 	} else {
@@ -30,121 +35,165 @@ fn print_error_message(message: &str) -> String {
 	}
 }
 
+/// Colorizes an auxiliary message, if color output is enabled.
+fn colorize_aux_message(message: &str) -> String {
+	if super::color_output_enabled() {
+		style(message).yellow().bold().to_string()
+	} else {
+		message.into()
+	}
+}
+
 /// Checks that all prerequisites are installed.
 ///
 /// Returns the versioned cargo command on success.
-pub(crate) fn check() -> Result<CargoCommandVersioned, String> {
-	let cargo_command = crate::get_cargo_command();
+pub(crate) fn check(target: RuntimeTarget) -> Result<CargoCommandVersioned, String> {
+	let cargo_command = crate::get_cargo_command(target);
+	match target {
+		RuntimeTarget::Wasm => {
+			if !cargo_command.supports_substrate_runtime_env(target) {
+				return Err(colorize_error_message(
+					"Cannot compile a WASM runtime: no compatible Rust compiler found!\n\
+					 Install at least Rust 1.68.0 or a recent nightly version.",
+				));
+			}
 
-	if !cargo_command.supports_substrate_wasm_env() {
-		return Err(print_error_message(
-			"Cannot compile the WASM runtime: no compatible Rust compiler found!\n\
-			 Install at least Rust 1.68.0 or a recent nightly version.",
-		))
+			check_wasm_toolchain_installed(cargo_command)
+		},
+		RuntimeTarget::Riscv => {
+			if !cargo_command.supports_substrate_runtime_env(target) {
+				return Err(colorize_error_message(
+					"Cannot compile a RISC-V runtime: no compatible Rust compiler found!\n\
+					 Install a toolchain from here and try again: https://github.com/paritytech/rustc-rv32e-toolchain/",
+				));
+			}
+
+			let dummy_crate = DummyCrate::new(&cargo_command, target);
+			let version = dummy_crate.get_rustc_version();
+			Ok(CargoCommandVersioned::new(cargo_command, version))
+		},
+	}
+}
+
+struct DummyCrate<'a> {
+	cargo_command: &'a CargoCommand,
+	temp: tempfile::TempDir,
+	manifest_path: PathBuf,
+	target: RuntimeTarget,
+}
+
+impl<'a> DummyCrate<'a> {
+	/// Creates a minimal dummy crate.
+	fn new(cargo_command: &'a CargoCommand, target: RuntimeTarget) -> Self {
+		let temp = tempdir().expect("Creating temp dir does not fail; qed");
+		let project_dir = temp.path();
+		fs::create_dir_all(project_dir.join("src")).expect("Creating src dir does not fail; qed");
+
+		let manifest_path = project_dir.join("Cargo.toml");
+		write_file_if_changed(
+			&manifest_path,
+			r#"
+				[package]
+				name = "dummy-crate"
+				version = "1.0.0"
+				edition = "2021"
+
+				[workspace]
+			"#,
+		);
+
+		write_file_if_changed(project_dir.join("src/main.rs"), "fn main() {}");
+		DummyCrate { cargo_command, temp, manifest_path, target }
 	}
 
-	check_wasm_toolchain_installed(cargo_command)
-}
-
-/// Creates a minimal dummy crate at the given path and returns the manifest path.
-fn create_minimal_crate(project_dir: &Path) -> std::path::PathBuf {
-	fs::create_dir_all(project_dir.join("src")).expect("Creating src dir does not fail; qed");
-
-	let manifest_path = project_dir.join("Cargo.toml");
-	write_file_if_changed(
-		&manifest_path,
-		r#"
-			[package]
-			name = "wasm-test"
-			version = "1.0.0"
-			edition = "2021"
-
-			[workspace]
-		"#,
-	);
-
-	write_file_if_changed(project_dir.join("src/main.rs"), "fn main() {}");
-	manifest_path
-}
-
-fn check_wasm_toolchain_installed(
-	cargo_command: CargoCommand,
-) -> Result<CargoCommandVersioned, String> {
-	let temp = tempdir().expect("Creating temp dir does not fail; qed");
-	let manifest_path = create_minimal_crate(temp.path()).display().to_string();
-
-	let prepare_command = |subcommand| {
-		let mut cmd = cargo_command.command();
+	fn prepare_command(&self, subcommand: &str) -> Command {
+		let mut cmd = self.cargo_command.command();
 		// Chdir to temp to avoid including project's .cargo/config.toml
 		// by accident - it can happen in some CI environments.
-		cmd.current_dir(&temp);
-		cmd.args(&[
-			subcommand,
-			"--target=wasm32-unknown-unknown",
-			"--manifest-path",
-			&manifest_path,
-		]);
+		cmd.current_dir(&self.temp);
+		cmd.arg(subcommand)
+			.arg(format!("--target={}", self.target.rustc_target()))
+			.args(&["--manifest-path", &self.manifest_path.display().to_string()]);
 
 		if super::color_output_enabled() {
 			cmd.arg("--color=always");
 		}
 
 		// manually set the `CARGO_TARGET_DIR` to prevent a cargo deadlock
-		let target_dir = temp.path().join("target").display().to_string();
+		let target_dir = self.temp.path().join("target").display().to_string();
 		cmd.env("CARGO_TARGET_DIR", &target_dir);
 
 		// Make sure the host's flags aren't used here, e.g. if an alternative linker is specified
 		// in the RUSTFLAGS then the check we do here will break unless we clear these.
 		cmd.env_remove("CARGO_ENCODED_RUSTFLAGS");
 		cmd.env_remove("RUSTFLAGS");
+		// Make sure if we're called from within a `build.rs` the host toolchain won't override a
+		// rustup toolchain we've picked.
+		cmd.env_remove("RUSTC");
 		cmd
-	};
-
-	let err_msg =
-		print_error_message("Rust WASM toolchain is not properly installed; please install it!");
-	let build_result = prepare_command("build").output().map_err(|_| err_msg.clone())?;
-	if !build_result.status.success() {
-		return match String::from_utf8(build_result.stderr) {
-			Ok(ref err) if err.contains("the `wasm32-unknown-unknown` target may not be installed") =>
-				Err(print_error_message("Cannot compile the WASM runtime: the `wasm32-unknown-unknown` target is not installed!\n\
-				                         You can install it with `rustup target add wasm32-unknown-unknown` if you're using `rustup`.")),
-
-			// Apparently this can happen when we're running on a non Tier 1 platform.
-			Ok(ref err) if err.contains("linker `rust-lld` not found") =>
-				Err(print_error_message("Cannot compile the WASM runtime: `rust-lld` not found!")),
-
-			Ok(ref err) => Err(format!(
-				"{}\n\n{}\n{}\n{}{}\n",
-				err_msg,
-				style("Further error information:").yellow().bold(),
-				style("-".repeat(60)).yellow().bold(),
-				err,
-				style("-".repeat(60)).yellow().bold(),
-			)),
-
-			Err(_) => Err(err_msg),
-		};
 	}
 
-	let mut run_cmd = prepare_command("rustc");
-	run_cmd.args(&["-q", "--", "--version"]);
+	fn get_rustc_version(&self) -> String {
+		let mut run_cmd = self.prepare_command("rustc");
+		run_cmd.args(&["-q", "--", "--version"]);
+		run_cmd
+			.output()
+			.ok()
+			.and_then(|o| String::from_utf8(o.stdout).ok())
+			.unwrap_or_else(|| "unknown rustc version".into())
+	}
 
-	let version = run_cmd
-		.output()
-		.ok()
-		.and_then(|o| String::from_utf8(o.stdout).ok())
-		.unwrap_or_else(|| "unknown rustc version".into());
-
-	if crate::build_std_required() {
-		let mut sysroot_cmd = prepare_command("rustc");
+	fn get_sysroot(&self) -> Option<String> {
+		let mut sysroot_cmd = self.prepare_command("rustc");
 		sysroot_cmd.args(&["-q", "--", "--print", "sysroot"]);
-		if let Some(sysroot) =
-			sysroot_cmd.output().ok().and_then(|o| String::from_utf8(o.stdout).ok())
-		{
+		sysroot_cmd.output().ok().and_then(|o| String::from_utf8(o.stdout).ok())
+	}
+
+	fn try_build(&self) -> Result<(), Option<String>> {
+		let Ok(result) = self.prepare_command("build").output() else { return Err(None) };
+		if !result.status.success() {
+			return Err(Some(String::from_utf8_lossy(&result.stderr).into()));
+		}
+		Ok(())
+	}
+}
+
+fn check_wasm_toolchain_installed(
+	cargo_command: CargoCommand,
+) -> Result<CargoCommandVersioned, String> {
+	let dummy_crate = DummyCrate::new(&cargo_command, RuntimeTarget::Wasm);
+
+	if let Err(error) = dummy_crate.try_build() {
+		let basic_error_message = colorize_error_message(
+			"Rust WASM toolchain is not properly installed; please install it!",
+		);
+		return match error {
+			None => Err(basic_error_message),
+			Some(error) if error.contains("the `wasm32-unknown-unknown` target may not be installed") => {
+				Err(colorize_error_message("Cannot compile the WASM runtime: the `wasm32-unknown-unknown` target is not installed!\n\
+				                         You can install it with `rustup target add wasm32-unknown-unknown` if you're using `rustup`."))
+			},
+			// Apparently this can happen when we're running on a non Tier 1 platform.
+			Some(ref error) if error.contains("linker `rust-lld` not found") =>
+				Err(colorize_error_message("Cannot compile the WASM runtime: `rust-lld` not found!")),
+			Some(error) => Err(format!(
+				"{}\n\n{}\n{}\n{}{}\n",
+				basic_error_message,
+				colorize_aux_message("Further error information:"),
+				colorize_aux_message(&"-".repeat(60)),
+				error,
+				colorize_aux_message(&"-".repeat(60)),
+			))
+		}
+	}
+
+	let version = dummy_crate.get_rustc_version();
+	if crate::build_std_required() {
+		if let Some(sysroot) = dummy_crate.get_sysroot() {
 			let src_path =
 				Path::new(sysroot.trim()).join("lib").join("rustlib").join("src").join("rust");
 			if !src_path.exists() {
-				return Err(print_error_message(
+				return Err(colorize_error_message(
 					"Cannot compile the WASM runtime: no standard library sources found!\n\
 					 You can install them with `rustup component add rust-src` if you're using `rustup`.",
 				))

substrate/utils/wasm-builder/src/wasm_project.rs

@@ -15,7 +15,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use crate::{write_file_if_changed, CargoCommandVersioned, OFFLINE};
+use crate::{write_file_if_changed, CargoCommandVersioned, RuntimeTarget, OFFLINE};
 
 use build_helper::rerun_if_changed;
 use cargo_metadata::{DependencyKind, Metadata, MetadataCommand};
@@ -112,6 +112,7 @@ fn crate_metadata(cargo_manifest: &Path) -> Metadata {
 ///
 /// The path to the compact runtime binary and the bloaty runtime binary.
 pub(crate) fn create_and_compile(
+	target: RuntimeTarget,
 	project_cargo_toml: &Path,
 	default_rustflags: &str,
 	cargo_cmd: CargoCommandVersioned,
@@ -120,11 +121,12 @@ pub(crate) fn create_and_compile(
 	check_for_runtime_version_section: bool,
 ) -> (Option<WasmBinary>, WasmBinaryBloaty) {
 	let runtime_workspace_root = get_wasm_workspace_root();
-	let runtime_workspace = runtime_workspace_root.join("wbuild");
+	let runtime_workspace = runtime_workspace_root.join(target.build_subdirectory());
 
 	let crate_metadata = crate_metadata(project_cargo_toml);
 
 	let project = create_project(
+		target,
 		project_cargo_toml,
 		&runtime_workspace,
 		&crate_metadata,
@@ -132,13 +134,58 @@ pub(crate) fn create_and_compile(
 		features_to_enable,
 	);
 
-	let build_config = BuildConfiguration::detect(&project);
+	let build_config = BuildConfiguration::detect(target, &project);
 
 	// Build the bloaty runtime blob
-	build_bloaty_blob(&build_config.blob_build_profile, &project, default_rustflags, cargo_cmd);
+	let raw_blob_path = build_bloaty_blob(
+		target,
+		&build_config.blob_build_profile,
+		&project,
+		default_rustflags,
+		cargo_cmd,
+	);
 
+	let (final_blob_binary, bloaty_blob_binary) = match target {
+		RuntimeTarget::Wasm => compile_wasm(
+			project_cargo_toml,
+			&project,
+			bloaty_blob_out_name_override,
+			check_for_runtime_version_section,
+			&build_config,
+		),
+		RuntimeTarget::Riscv => {
+			let out_name = bloaty_blob_out_name_override
+				.unwrap_or_else(|| get_blob_name(target, project_cargo_toml));
+			let out_path = project.join(format!("{out_name}.polkavm"));
+			fs::copy(raw_blob_path, &out_path).expect("copying the runtime blob should never fail");
+			(None, WasmBinaryBloaty(out_path))
+		},
+	};
+
+	generate_rerun_if_changed_instructions(
+		project_cargo_toml,
+		&project,
+		&runtime_workspace,
+		final_blob_binary.as_ref(),
+		&bloaty_blob_binary,
+	);
+
+	if let Err(err) = adjust_mtime(&bloaty_blob_binary, final_blob_binary.as_ref()) {
+		build_helper::warning!("Error while adjusting the mtime of the blob binaries: {}", err)
+	}
+
+	(final_blob_binary, bloaty_blob_binary)
+}
+
+fn compile_wasm(
+	project_cargo_toml: &Path,
+	project: &Path,
+	bloaty_blob_out_name_override: Option<String>,
+	check_for_runtime_version_section: bool,
+	build_config: &BuildConfiguration,
+) -> (Option<WasmBinary>, WasmBinaryBloaty) {
 	// Get the name of the bloaty runtime blob.
-	let bloaty_blob_default_name = get_blob_name(project_cargo_toml);
+	let bloaty_blob_default_name = get_blob_name(RuntimeTarget::Wasm, project_cargo_toml);
 	let bloaty_blob_out_name =
 		bloaty_blob_out_name_override.unwrap_or_else(|| bloaty_blob_default_name.clone());
 
@@ -183,19 +230,6 @@ pub(crate) fn create_and_compile(
 	});
 
 	let final_blob_binary = compact_compressed_blob_path.or(compact_blob_path);
-
-	generate_rerun_if_changed_instructions(
-		project_cargo_toml,
-		&project,
-		&runtime_workspace,
-		final_blob_binary.as_ref(),
-		&bloaty_blob_binary,
-	);
-
-	if let Err(err) = adjust_mtime(&bloaty_blob_binary, final_blob_binary.as_ref()) {
-		build_helper::warning!("Error while adjusting the mtime of the blob binaries: {}", err)
-	}
-
 	(final_blob_binary, bloaty_blob_binary)
 }
 
@@ -314,8 +348,12 @@ fn get_crate_name(cargo_manifest: &Path) -> String {
 }
 
 /// Returns the name for the blob binary.
-fn get_blob_name(cargo_manifest: &Path) -> String {
-	get_crate_name(cargo_manifest).replace('-', "_")
+fn get_blob_name(target: RuntimeTarget, cargo_manifest: &Path) -> String {
+	let crate_name = get_crate_name(cargo_manifest);
+	match target {
+		RuntimeTarget::Wasm => crate_name.replace('-', "_"),
+		RuntimeTarget::Riscv => crate_name,
+	}
 }
 
 /// Returns the root path of the wasm workspace.
@@ -336,6 +374,7 @@ fn get_wasm_workspace_root() -> PathBuf {
 }
 
 fn create_project_cargo_toml(
+	target: RuntimeTarget,
 	wasm_workspace: &Path,
 	workspace_root_path: &Path,
 	crate_name: &str,
@@ -396,17 +435,18 @@ fn create_project_cargo_toml(
 	}
 
 	let mut package = Table::new();
-	package.insert("name".into(), format!("{}-wasm", crate_name).into());
+	package.insert("name".into(), format!("{}-blob", crate_name).into());
 	package.insert("version".into(), "1.0.0".into());
 	package.insert("edition".into(), "2021".into());
 
 	wasm_workspace_toml.insert("package".into(), package.into());
 
-	let mut lib = Table::new();
-	lib.insert("name".into(), wasm_binary.into());
-	lib.insert("crate-type".into(), vec!["cdylib".to_string()].into());
-
-	wasm_workspace_toml.insert("lib".into(), lib.into());
+	if target == RuntimeTarget::Wasm {
+		let mut lib = Table::new();
+		lib.insert("name".into(), wasm_binary.into());
+		lib.insert("crate-type".into(), vec!["cdylib".to_string()].into());
+		wasm_workspace_toml.insert("lib".into(), lib.into());
+	}
 
 	let mut dependencies = Table::new();
 
@@ -527,6 +567,7 @@ fn has_runtime_wasm_feature_declared(
 ///
 /// The path to the created wasm project.
 fn create_project(
+	target: RuntimeTarget,
 	project_cargo_toml: &Path,
 	wasm_workspace: &Path,
 	crate_metadata: &Metadata,
@@ -535,7 +576,7 @@ fn create_project(
 ) -> PathBuf {
 	let crate_name = get_crate_name(project_cargo_toml);
 	let crate_path = project_cargo_toml.parent().expect("Parent path exists; qed");
-	let wasm_binary = get_blob_name(project_cargo_toml);
+	let wasm_binary = get_blob_name(target, project_cargo_toml);
 	let wasm_project_folder = wasm_workspace.join(&crate_name);
 
 	fs::create_dir_all(wasm_project_folder.join("src"))
@@ -552,6 +593,7 @@ fn create_project(
 	enabled_features.extend(features_to_enable.into_iter());
 
 	create_project_cargo_toml(
+		target,
 		&wasm_project_folder,
 		workspace_root_path,
 		&crate_name,
@@ -560,10 +602,20 @@ fn create_project(
 		enabled_features.into_iter(),
 	);
 
-	write_file_if_changed(
-		wasm_project_folder.join("src/lib.rs"),
-		"#![no_std] pub use wasm_project::*;",
-	);
+	match target {
+		RuntimeTarget::Wasm => {
+			write_file_if_changed(
+				wasm_project_folder.join("src/lib.rs"),
+				"#![no_std] pub use wasm_project::*;",
+			);
+		},
+		RuntimeTarget::Riscv => {
+			write_file_if_changed(
+				wasm_project_folder.join("src/main.rs"),
+				"#![no_std] #![no_main] pub use wasm_project::*;",
+			);
+		},
+	}
 
 	if let Some(crate_lock_file) = find_cargo_lock(project_cargo_toml) {
 		// Use the `Cargo.lock` of the main project.
@@ -641,14 +693,15 @@ impl BuildConfiguration {
 	/// # Note
 	///
 	/// Can be overriden by setting [`crate::WASM_BUILD_TYPE_ENV`].
-	fn detect(wasm_project: &Path) -> Self {
+	fn detect(target: RuntimeTarget, wasm_project: &Path) -> Self {
 		let (name, overriden) = if let Ok(name) = env::var(crate::WASM_BUILD_TYPE_ENV) {
 			(name, true)
 		} else {
 			// First go backwards to the beginning of the target directory.
-			// Then go forwards to find the "wbuild" directory.
+			// Then go forwards to find the build subdirectory.
 			// We need to go backwards first because when starting from the root there
-			// might be a chance that someone has a "wbuild" directory somewhere in the path.
+			// might be a chance that someone has a directory somewhere in the path with the same
+			// name.
 			let name = wasm_project
 				.components()
 				.rev()
@@ -656,9 +709,9 @@ impl BuildConfiguration {
 				.collect::<Vec<_>>()
 				.iter()
 				.rev()
-				.take_while(|c| c.as_os_str() != "wbuild")
+				.take_while(|c| c.as_os_str() != target.build_subdirectory())
 				.last()
-				.expect("We put the wasm project within a `target/.../wbuild` path; qed")
+				.expect("We put the runtime project within a `target/.../[rw]build` path; qed")
 				.as_os_str()
 				.to_str()
 				.expect("All our profile directory names are ascii; qed")
@@ -711,22 +764,34 @@ fn offline_build() -> bool {
 
 /// Build the project and create the bloaty runtime blob.
 fn build_bloaty_blob(
+	target: RuntimeTarget,
 	blob_build_profile: &Profile,
 	project: &Path,
 	default_rustflags: &str,
 	cargo_cmd: CargoCommandVersioned,
-) {
+) -> PathBuf {
 	let manifest_path = project.join("Cargo.toml");
 	let mut build_cmd = cargo_cmd.command();
 
-	let rustflags = format!(
-		"-C target-cpu=mvp -C target-feature=-sign-ext -C link-arg=--export-table {} {}",
-		default_rustflags,
-		env::var(crate::WASM_BUILD_RUSTFLAGS_ENV).unwrap_or_default(),
-	);
+	let mut rustflags = String::new();
+	match target {
+		RuntimeTarget::Wasm => {
+			rustflags.push_str(
+				"-C target-cpu=mvp -C target-feature=-sign-ext -C link-arg=--export-table ",
+			);
+		},
+		RuntimeTarget::Riscv => {
+			rustflags.push_str("-C target-feature=+lui-addi-fusion -C relocation-model=pie -C link-arg=--emit-relocs -C link-arg=--unique ");
+		},
+	}
+
+	rustflags.push_str(default_rustflags);
+	rustflags.push_str(" --cfg substrate_runtime ");
+	rustflags.push_str(&env::var(crate::WASM_BUILD_RUSTFLAGS_ENV).unwrap_or_default());
 
 	build_cmd
-		.args(&["rustc", "--target=wasm32-unknown-unknown"])
+		.arg("rustc")
+		.arg(format!("--target={}", target.rustc_target()))
 		.arg(format!("--manifest-path={}", manifest_path.display()))
 		.env("RUSTFLAGS", rustflags)
 		// Manually set the `CARGO_TARGET_DIR` to prevent a cargo deadlock (cargo locks a target dir
@@ -737,6 +802,9 @@ fn build_bloaty_blob(
 		// our own `RUSTFLAGS` and thus, we need to remove this. Otherwise cargo favors this
 		// env variable.
 		.env_remove("CARGO_ENCODED_RUSTFLAGS")
+		// Make sure if we're called from within a `build.rs` the host toolchain won't override a
+		// rustup toolchain we've picked.
+		.env_remove("RUSTC")
 		// We don't want to call ourselves recursively
 		.env(crate::SKIP_BUILD_ENV, "");
 
@@ -778,6 +846,52 @@ fn build_bloaty_blob(
 	if build_cmd.status().map(|s| s.success()).is_err() {
 		process::exit(1);
 	}
+
+	let blob_name = get_blob_name(target, &manifest_path);
+	let target_directory = project
+		.join("target")
+		.join(target.rustc_target())
+		.join(blob_build_profile.directory());
+	match target {
+		RuntimeTarget::Riscv => {
+			let elf_path = target_directory.join(&blob_name);
+			let elf_metadata = match elf_path.metadata() {
+				Ok(path) => path,
+				Err(error) =>
+					panic!("internal error: couldn't read the metadata of {elf_path:?}: {error}"),
+			};
+
+			let polkavm_path = target_directory.join(format!("{}.polkavm", blob_name));
+			if polkavm_path
+				.metadata()
+				.map(|polkavm_metadata| {
+					polkavm_metadata.modified().unwrap() >= elf_metadata.modified().unwrap()
+				})
+				.unwrap_or(true)
+			{
+				let blob_bytes =
+					std::fs::read(elf_path).expect("binary always exists after its built");
+
+				let mut config = polkavm_linker::Config::default();
+				config.set_strip(true); // TODO: This shouldn't always be done.
+
+				let program = match polkavm_linker::program_from_elf(config, &blob_bytes) {
+					Ok(program) => program,
+					Err(error) => {
+						println!("Failed to link the runtime blob; this is probably a bug!");
+						println!("Linking error: {error}");
+						process::exit(1);
+					},
+				};
+
+				std::fs::write(&polkavm_path, program.as_bytes())
+					.expect("writing the blob to a file always works");
+			}
+
+			polkavm_path
+		},
+		RuntimeTarget::Wasm => target_directory.join(format!("{}.wasm", blob_name)),
+	}
 }
 
 fn compact_wasm(
@@ -786,7 +900,7 @@ fn compact_wasm(
 	cargo_manifest: &Path,
 	out_name: &str,
 ) -> Option<WasmBinary> {
-	let default_out_name = get_blob_name(cargo_manifest);
+	let default_out_name = get_blob_name(RuntimeTarget::Wasm, cargo_manifest);
 	let in_path = project
 		.join("target/wasm32-unknown-unknown")
 		.join(inner_profile.directory())
@@ -973,6 +1087,7 @@ fn generate_rerun_if_changed_instructions(
 	println!("cargo:rerun-if-env-changed={}", crate::WASM_TARGET_DIRECTORY);
 	println!("cargo:rerun-if-env-changed={}", crate::WASM_BUILD_TOOLCHAIN);
 	println!("cargo:rerun-if-env-changed={}", crate::WASM_BUILD_STD);
+	println!("cargo:rerun-if-env-changed={}", crate::RUNTIME_TARGET);
 }
 
 /// Track files and paths related to the given package to rerun `build.rs` on any relevant change.
@@ -1018,7 +1133,7 @@ fn copy_blob_to_target_directory(cargo_manifest: &Path, blob_binary: &WasmBinary
 
 	fs::copy(
 		blob_binary.wasm_binary_path(),
-		target_dir.join(format!("{}.wasm", get_blob_name(cargo_manifest))),
+		target_dir.join(format!("{}.wasm", get_blob_name(RuntimeTarget::Wasm, cargo_manifest))),
 	)
 	.expect("Copies blob binary to `WASM_TARGET_DIRECTORY`.");
 }