split build.rs into runtime-specific and root

In runtime we need to get the linker scripts somewhere that the linker
can use them. We _always_ need libtock_layout.ld, and we may want the
board-specific ld scripts.

In the new crate for build.rs, we specify which linker script we
actually want.

Author: bradjc

libtock_runtime_build/src/lib.rs

@@ -27,10 +27,6 @@ pub fn auto_layout() {
         "Build path contains a newline, which is unsupported"
     );
 
-    // Point the linker to the generic libtock-rs linker file.
-    let generic_ld_dir: PathBuf = ["runtime"].iter().collect();
-    println!("cargo:rustc-link-search={}", generic_ld_dir.display());
-
     // Choose the linker file we are going to use for this build. That can be
     // specified by choosing a platform, where the linker file will be selected
     // from `runtime/layouts`, or by explicitly setting the flash and RAM
@@ -47,16 +43,7 @@ pub fn auto_layout() {
     if let Ok(platform) = platform {
         // Point the linker to the correct platform-specific linker file.
         let platform_ld_name = format!("{}.ld", platform);
-        let platform_ld_dir: PathBuf = ["runtime", "layouts"].iter().collect();
-        let platform_ld_path: PathBuf = ["runtime", "layouts", &platform_ld_name].iter().collect();
-
-        assert!(platform_ld_path.exists(), "Unknown platform {}", platform);
-
-        println!("cargo:rerun-if-changed={}", platform_ld_path.display());
         println!("cargo:rustc-link-arg=-T{}", platform_ld_name);
-
-        // Tell rustc where to search for the layout file.
-        println!("cargo:rustc-link-search={}", platform_ld_dir.display());
     } else if let (Ok(linker_flash), Ok(linker_ram)) = (linker_flash, linker_ram) {
         // Create a valid linker file with the specified flash and ram locations.
         //

runtime/Cargo.toml

@@ -14,11 +14,6 @@ libtock_platform = { path = "../platform" }
 
 [features]
 
-# By default, libtock_runtime looks for the LIBTOCK_PLATFORM variable to decide
-# what layout file to use. If you are providing your own linker script, set
-# no_auto_layout to disable the layout file logic.
-no_auto_layout = []
-
 # By default, libtock_runtime calls Memop to tell the Tock kernel where the
 # stack and heap begin. The kernel uses those addresses to specify the stack and
 # heap address ranges if the process faults. Those calls cost 22 bytes on ARM

runtime/build.rs

@@ -0,0 +1,40 @@
+//! This build.rs makes common linker scripts available when linking libtock-rs
+//! apps.
+
+fn main() {
+    use std::fs::copy;
+    use std::fs::read_dir;
+    use std::path::PathBuf;
+
+    const LAYOUT_GENERIC_FILENAME: &str = "libtock_layout.ld";
+
+    // Note: cargo fails if run in a path that is not valid Unicode, so this
+    // script doesn't need to handle non-Unicode paths. Also, OUT_DIR cannot be
+    // in a location with a newline in it, or we have no way to pass
+    // rustc-link-search to cargo.
+    let out_dir = &std::env::var("OUT_DIR").expect("Unable to read OUT_DIR");
+    assert!(
+        !out_dir.contains('\n'),
+        "Build path contains a newline, which is unsupported"
+    );
+
+    // Copy all platform linker scripts to a directory where the linker can find
+    // them.
+    let paths = read_dir("layouts").unwrap();
+    for path in paths {
+        let ld_path = path.as_ref().unwrap().path();
+        let ld_name = path.as_ref().unwrap().file_name().into_string().unwrap();
+        let out_ld_path: PathBuf = [out_dir, &ld_name].iter().collect();
+        copy(ld_path, out_ld_path).expect("Unable to copy platform layout into OUT_DIR");
+    }
+
+    // Copy the generic layout file into OUT_DIR.
+    let out_layout_generic: PathBuf = [out_dir, LAYOUT_GENERIC_FILENAME].iter().collect();
+    println!("cargo:rerun-if-changed={}", LAYOUT_GENERIC_FILENAME);
+    copy(LAYOUT_GENERIC_FILENAME, out_layout_generic)
+        .expect("Unable to copy layout_generic.ld into OUT_DIR");
+
+    // Tell the linker that it can find linker scripts in the out directory of
+    // the libtock_runtime crate.
+    println!("cargo:rustc-link-search={}", out_dir);
+}