Merge #159

159: build.rs: Migrate to CARGO_ENCODED_RUSTFLAGS r=stlankes a=mkroening

Fixes #158.

Cargo introduced `CARGO_ENCODED_RUSTFLAGS` in rust-lang/cargo#9601 to make setting flags less error prone – it encodes arguments separated by `0x1f` (ASCII Unit Separator), instead of white spaces (old `RUSTFLAGS`).

`CARGO_ENCODED_RUSTFLAGS` are preferred over the old `RUSTFLAGS` in cargo. For build scripts, cargo converts its `RUSTFLAGS` to `CARGO_ENCODED_RUSTFLAGS`. For unset `RUSTFLAGS` it is set to an empty string. Thus our build script would call cargo for building libhermit-rs with a set – but empty – `CARGO_ENCODED_RUSTFLAGS`, which takes precedence over our prepared `RUSTFLAGS`. Specifically this caused our `-Zmutable-noalias=no` flag to be ignored, causing the same network issue as #128 again.

This PR adjusts our build script to make direct use of `CARGO_ENCODED_RUSTFLAGS`, the new and preferred way of handling flags in build scripts. This causes our flags to be correctly handled again.

Co-authored-by: Martin Kröning <mkroening@posteo.net>

hermit-sys/build.rs

@@ -98,30 +98,29 @@ fn build_hermit(src_dir: &Path, target_dir_opt: Option<&Path>) {
 	}
 
 	let mut rustflags = vec!["-Zmutable-noalias=no".to_string()];
+	let outer_rustflags = env::var("CARGO_ENCODED_RUSTFLAGS").unwrap();
 
 	#[cfg(feature = "instrument")]
 	{
 		rustflags.push("-Zinstrument-mcount".to_string());
-		// Add outer `RUSTFLAGS` to command
-		if let Ok(var) = env::var("RUSTFLAGS") {
-			rustflags.push(var);
-		}
+		// Add outer rustflags to command
+		rustflags.push(outer_rustflags);
 	}
 
 	#[cfg(not(feature = "instrument"))]
 	{
 		// If the `instrument` feature feature is not enabled,
-		// filter it from outer `RUSTFLAGS` before adding them to the command.
-		if let Ok(var) = env::var("RUSTFLAGS") {
-			let flags = var
-				.split(',')
+		// filter it from outer rustflags before adding them to the command.
+		if !outer_rustflags.is_empty() {
+			let flags = outer_rustflags
+				.split('\x1f')
 				.filter(|&flag| !flag.contains("instrument-mcount"))
 				.map(String::from);
 			rustflags.extend(flags);
 		}
 	}
 
-	cmd.env("RUSTFLAGS", rustflags.join(" "));
+	cmd.env("CARGO_ENCODED_RUSTFLAGS", rustflags.join("\x1f"));
 
 	let status = cmd.status().expect("failed to start kernel build");
 	assert!(status.success());