From 465da6e7cd6a81f37e6fe4bbe9caacc51d41a11f Mon Sep 17 00:00:00 2001
From: pantonshire <tom@tomandtally.co.uk>
Date: Sun, 25 Aug 2024 11:15:11 +0100
Subject: [PATCH] build asm in build.rs

---
 boot1/asm/prelude.s |   6 ++
 boot1/build.rs      | 153 ++++++++++++++++++++++++++++++++++++++++++++
 boot1/link.ld       |   1 +
 3 files changed, 160 insertions(+)
 create mode 100644 boot1/asm/prelude.s

diff --git a/boot1/asm/prelude.s b/boot1/asm/prelude.s
new file mode 100644
index 0000000..04b2e71
--- /dev/null
+++ b/boot1/asm/prelude.s
@@ -0,0 +1,6 @@
+%include "defines.s"
+
+[org BOOT1_LOADPOINT]
+[bits 16]
+
+hlt
diff --git a/boot1/build.rs b/boot1/build.rs
index 3bd445e..d9b35c9 100644
--- a/boot1/build.rs
+++ b/boot1/build.rs
@@ -1,4 +1,157 @@
+use std::{env, ffi::{OsStr, OsString}, fmt, fs, io, path::{Path, PathBuf}, process::{self, Command}};
+
 fn main() {
+  let out_dir = env::var_os("OUT_DIR")
+    .expect("OUT_DIR not set");
+  let out_dir = PathBuf::from(out_dir);
+
+  let path = SearchPath::load();
+  
+  let nasm_path = path.search("nasm")
+    .next()
+    .expect("failed to find nasm in PATH");
+  let nasm = Nasm::new(nasm_path);
+
+  build_asm(&nasm, &out_dir);
+  
+  emit_link_args();  
+
+  rerun_if_changed("build.rs".as_ref());
+}
+
+fn emit_link_args() {
   println!("cargo::rustc-link-arg=-Tlink.ld");
 }
 
+fn rerun_if_changed(path: &Path) {
+  if let Some(path_str) = path.to_str() {
+    println!("cargo::rerun-if-changed={}", path_str);
+  }
+  else {
+    eprintln!("invalid unicode file path");
+  }
+}
+
+fn build_asm(nasm: &Nasm, out_dir: &Path) {
+  nasm.assemble(
+    &out_dir.join("prelude.bin"),
+    &["asm/prelude.s".as_ref()],
+    &["..".as_ref()],
+  ).unwrap();
+}
+
+struct Nasm {
+  bin_path: PathBuf,
+}
+
+impl Nasm {
+  fn new(bin_path: PathBuf) -> Self {
+    Self { bin_path }
+  }
+
+  fn assemble(&self, output: &Path, sources: &[&Path], includes: &[&Path]) -> Result<(), CmdError>
+  {
+    for source in sources {
+      rerun_if_changed(source);
+    }
+
+    let mut cmd = Command::new(&self.bin_path);
+    cmd.arg("-f").arg("bin");
+
+    for include in includes {
+      let mut buf = OsString::new();
+      buf.push("-I");
+      buf.push(include);
+      cmd.arg(buf);
+    }
+
+    cmd
+      .arg("-o")
+      .arg(output)
+      .args(sources);
+
+    run_cmd(&mut cmd)?;
+
+    Ok(())
+  }
+}
+
+struct SearchPath {
+  paths: Vec<PathBuf>
+}
+
+impl SearchPath {
+  fn load() -> Self {
+    let path_var = env::var_os("PATH").unwrap_or_default();
+    let paths = env::split_paths(&path_var).collect();
+    Self { paths }
+  }
+  
+  fn search<'a, 'b, 'c, T>(&'a self, bin: &'b T) -> impl Iterator<Item = PathBuf> + 'c
+  where
+    'a: 'c,
+    'b: 'c,
+    T: AsRef<OsStr> + ?Sized,
+  {
+    let bin = bin.as_ref();
+    self.paths
+      .iter()
+      .filter_map(move |path| {
+        let path = path.join(bin);
+        fs::metadata(&path)
+          .ok()
+          .and_then(|meta| if meta.is_file() || meta.is_symlink() {
+            Some(path)
+          } else {
+            None
+          })
+      })
+  }
+}
+
+fn run_cmd(cmd: &mut Command) -> Result<process::Output, CmdError> {
+  use fmt::Write;
+
+  cmd
+      .output()
+      .map_err(CmdErrorKind::Io)
+      .and_then(|out| if out.status.success() {
+        Ok(out)
+      } else {
+        Err(CmdErrorKind::Status(out))
+      })
+      .map_err(|err| {
+        let mut cmd_buf = String::new();
+        write!(&mut cmd_buf, "{:?}", cmd).ok();
+        CmdError::new(cmd_buf, err)
+      })
+}
+
+#[derive(Debug)]
+struct CmdError {
+  cmd: String,
+  kind: CmdErrorKind,
+}
+
+impl CmdError {
+  fn new(cmd: String, kind: CmdErrorKind) -> Self {
+    Self { cmd, kind }
+  }
+}
+
+impl fmt::Display for CmdError {
+  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    write!(f, "`{}` failed: ", self.cmd)?;
+    match &self.kind {
+      CmdErrorKind::Io(err) => err.fmt(f),
+      CmdErrorKind::Status(out) => write!(f, "exited with status {}", out.status),
+    }
+  }
+}
+
+#[derive(Debug)]
+enum CmdErrorKind {
+  Io(io::Error),
+  Status(process::Output),
+}
+
diff --git a/boot1/link.ld b/boot1/link.ld
index 28c7f94..c77e0b0 100644
--- a/boot1/link.ld
+++ b/boot1/link.ld
@@ -3,6 +3,7 @@ OUTPUT_FORMAT("binary")
 SECTIONS {
   .text : { *(.text); *(.text.*) }
   .data : { *(.data); *(.data.*) }
+  .bss : { *(.bss); *(.bss.*) }
   .rodata : { *(.rodata); *(.rodata.*) }
 }