move runtime to own crate, add _start, and use build script for config

bril-rs/brillvm/Cargo.toml

@@ -1,3 +1,4 @@
+workspace = { members = ["runtime"] }
 [package]
 name = "brillvm"
 version = "0.1.0"
@@ -19,16 +20,11 @@ clap = { version = "4.4", features = ["derive"] }
 inkwell = { git = "https://github.com/TheDan64/inkwell.git", features = [
     "llvm18-0",
 ] }
-libc-print = "0.1"
 
 [dependencies.bril-rs]
 path = ".."
 features = ["float", "ssa", "memory"]
 
-[[bin]]
-name = "rt"
-path = "bin/rt.rs"
-
 # Need to set a default `main` to build `rt` bin
 [[bin]]
 name = "main"

bril-rs/brillvm/Makefile

@@ -19,16 +19,16 @@ clean:
 
 .PHONY: rt
 rt:
-	cargo rustc --bin rt --release -- --emit=llvm-bc && mv target/release/deps/rt-*.bc rt.bc
+	cd runtime && cargo rustc --release -- --emit=llvm-bc && mv ../target/release/deps/runtime-*.bc ../rt.bc
 
 example:
 # bril2json < ../../benchmarks/mem/sieve.bril | cargo run -- -i 100
 	bril2json < ../../benchmarks/mixed/cholesky.bril | cargo run -- -i
 
 .PHONY: test
-test: build rt
+test:
 	turnt -e brillvm $(TESTS)
 
 .PHONY: benchmark
-benchmark: build rt
+benchmark:
 	turnt -e brillvm $(BENCHMARKS)

bril-rs/brillvm/runtime/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "runtime"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+libc-print = "0.1"

bril-rs/brillvm/runtime/build.rs

@@ -0,0 +1,11 @@
+fn main() {
+    #[cfg(target_os = "linux")]
+    println!("cargo:rustc-link-arg=-nostdlib");
+    #[cfg(target_os = "macos")]
+    println!("cargo:rustc-link-arg=-undefined");
+    #[cfg(target_os = "macos")]
+    println!("cargo:rustc-link-arg=dynamic_lookup");
+
+    #[cfg(not(any(target_os = "linux", target_os = "macos")))]
+    assert!(false)
+}

bril-rs/brillvm/bin/rt.rs → bril-rs/brillvm/runtime/src/main.rs

@@ -72,6 +72,11 @@ pub unsafe extern "C" fn _bril_parse_float(arg: *const c_char) -> f64 {
     r_str.parse::<f64>().unwrap()
 }
 
+#[no_mangle]
+pub extern "C" fn _start() -> ! {
+    loop {}
+}
+
 #[cfg(not(test))]
 #[panic_handler]
 fn my_panic(_info: &core::panic::PanicInfo) -> ! {