link in the prelude object

boot1/asm/prelude.s

@@ -1,7 +1,12 @@
 %include "defines.s"
 
-[org BOOT1_LOADPOINT]
 [bits 16]
 
+section .prelude
+
+extern boot1_bin_len
+
+global prelude
 prelude:
   hlt
+  dd boot1_bin_len

boot1/build.rs

@@ -20,24 +20,31 @@ fn main() {
 }
 
 fn emit_link_args() {
-  println!("cargo::rustc-link-arg=-Tlink.ld");
+  let linker_script_path = "link.ld";
+  println!("cargo::rustc-link-arg=-T{}", linker_script_path);
+  rerun_if_changed(linker_script_path.as_ref());
 }
 
 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");
-  }
+  let path_str = path.to_str()
+    .expect("expected path to be valid utf8");
+  println!("cargo::rerun-if-changed={}", path_str);
+}
+
+fn link_obj(path: &Path) {
+  let path_str = path.to_str()
+    .expect("expected path to be valid utf8");
+  println!("cargo::rustc-link-arg={}", path_str);
 }
 
 fn build_asm(nasm: &Nasm, out_dir: &Path) {
+  let prelude_obj_path = out_dir.join("prelude.o");
   nasm.assemble(
-    &out_dir.join("prelude.bin"),
+    &prelude_obj_path,
     &["asm/prelude.s".as_ref()],
     &["../include".as_ref()],
   ).unwrap();
+  link_obj(&prelude_obj_path);
 }
 
 struct Nasm {
@@ -57,9 +64,9 @@ impl Nasm {
 
     let mut cmd = Command::new(&self.bin_path);
     cmd
+      .arg("-Werror")
       .arg("-f")
-      .arg("bin")
-      .arg("-Werror");
+      .arg("elf");
 
     for include in includes {
       let mut buf = OsString::new();

boot1/link.ld

@@ -1,10 +1,34 @@
 OUTPUT_FORMAT("binary")
-. = 0x9000;
-SECTIONS {
-  .text : { *(.text); *(.text.*) }
-  .data : { *(.data); *(.data.*) }
-  .bss : { *(.bss); *(.bss.*) }
-  .rodata : { *(.rodata); *(.rodata.*) }
-}
 
+. = 0x8200;
 
+SECTIONS {
+  .prelude : {
+    *(.prelude)
+  }
+  
+  .text : {
+    *(.text)
+    *(.text.*)
+  }
+  
+  .data : {
+    *(.data)
+    *(.data.*)
+  }
+  
+  .bss : {
+    *(.bss)
+    *(.bss.*)
+  }
+  
+  .rodata : {
+    *(.rodata)
+    *(.rodata.*)
+  }
+  
+  /* Define a symbol for the total length of the binary, so the prelude knows how many blocks to
+   * load from disk.
+   */
+  boot1_bin_len = . - 0x8200;
+}

boot1/src/main.rs

@@ -10,6 +10,10 @@ const VGA_ADDR: usize = 0xb8000;
 
 const STR: &[u8] = b"the quick brown fox jumps over the lazy dog";
 
+extern "C" {
+  fn prelude() -> !;
+}
+
 #[panic_handler]
 fn panic(_info: &PanicInfo) -> ! {
   hlt()
@@ -43,7 +47,8 @@ pub extern "C" fn _start() -> ! {
 
   vga_buf[0] = 0x1f02; //smiley
 
-  hlt()
+  // hlt()
+  unsafe { prelude() };
 }
 
 #[inline]