[sail-riscv] add sail-riscv Rust binder

Disambiguation:

* sail: the official sail language, library, API, headers that belongs
  to rem-project.
* sail-riscv: the riscv spec definition describe using sail.

Build step:

1. Use rust-bindgen to create Rust FFI to the sail header, so that we
   can always keep integrity of the sail library.
2. Extern declare all necessary C function define in generated model
   from sail and sail-riscv.
3. Define or override necessary functions from our Rust side.

Current issues:

* Implement our Rust emulator using above strategy inevitably create a
  programming model that functions will be called back and forth from
  both C and Rust side. This will also make the code hard to read. Hope
  this situation could be improved in upcomming rational documents.
* Although sail support using different prefix for its model declaration
  when generating C sources, I am still afraid that these global machine
  state in sail-riscv model will cause problem in our future development.

Signed-off-by: Avimitin <[email protected]>

nix/overlay.nix

@@ -21,6 +21,7 @@ rec {
   libspike_interfaces = final.callPackage ../difftest/spike_interfaces { };
 
   sail-riscv-c-model = final.callPackage ./pkgs/sail-riscv-c-model.nix { };
+  sail-riscv-rust-emu = final.callPackage ../sail-riscv { };
 
   # DynamoCompiler doesn't support python 3.12+ yet
   buddy-mlir = final.callPackage ./pkgs/buddy-mlir.nix { python3 = final.python311; };

sail-riscv/default.nix

@@ -0,0 +1,4 @@
+{ lib, newScope }:
+lib.makeScope newScope (scope: {
+  sail-riscv-sys = scope.callPackage ./sail-riscv-sys { };
+})

sail-riscv/sail-riscv-sys/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "sail-riscv-sys"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+
+[build-dependencies]
+bindgen = "0.70.1"

sail-riscv/sail-riscv-sys/build.rs

@@ -0,0 +1,19 @@
+use std::env;
+use std::path::PathBuf;
+
+fn main() {
+    let sail_install_path = env::var("SAIL_INSTALL_PATH").expect("$SAIL_INSTALL_PATH not set");
+
+    let bindings = bindgen::Builder::default()
+        .header("sail_include/wrapper.h")
+        .clang_arg(format!("-I{sail_install_path}/share/sail/lib"))
+        .parse_callbacks(Box::new(bindgen::CargoCallbacks::new()))
+        .generate()
+        .expect("Unable to generate bindings");
+
+    // Write the bindings to the $OUT_DIR/bindings.rs file.
+    let out_path = PathBuf::from(env::var("OUT_DIR").unwrap());
+    bindings
+        .write_to_file(out_path.join("sail_h.rs"))
+        .expect("Couldn't write bindings!");
+}

sail-riscv/sail-riscv-sys/default.nix

@@ -0,0 +1,47 @@
+{ lib
+, rustPlatform
+, sail-riscv-c-model
+, rustfmt
+, rust-analyzer
+, gmp
+}:
+
+let
+  finalPkg = rustPlatform.buildRustPackage {
+    name = "sail-riscv-rs-emulator";
+    src = with lib.fileset; toSource {
+      root = ./.;
+      fileset = unions [
+        ./src
+        ./build.rs
+        ./sail_include
+        ./Cargo.lock
+        ./Cargo.toml
+      ];
+    };
+
+    nativeBuildInputs = [
+      rustPlatform.bindgenHook
+    ];
+
+    buildInputs = [ gmp ];
+
+    env = {
+      SAIL_INSTALL_PATH = toString sail-riscv-c-model.sail;
+    };
+
+    cargoLock = {
+      lockFile = ./Cargo.lock;
+    };
+
+    passthru = {
+      devShell = finalPkg.overrideAttrs (prev: {
+        nativeBuildInputs = prev.nativeBuildInputs ++ [
+          rustfmt
+          rust-analyzer
+        ];
+      });
+    };
+  };
+in
+finalPkg

sail-riscv/sail-riscv-sys/sail_include/wrapper.h

@@ -0,0 +1 @@
+#include <sail.h>