stage1: add header

stage1/build.rs

@@ -1,3 +1,4 @@
+use std::ffi::OsStr;
 use std::path::Path;
 
 fn main() {
@@ -5,4 +6,14 @@ fn main() {
 
     let ld_script_path = manifest_dir.join("stage1.ld");
     println!("cargo:rustc-link-arg=--script={}", ld_script_path.display());
+    println!("cargo:rerun-if-changed={}", ld_script_path.display());
+
+    let asm_dir = manifest_dir.join("src").join("asm");
+    let files = asm_dir.read_dir().unwrap();
+    for entry in files {
+        let path = entry.unwrap().path();
+        if path.extension() == Some(OsStr::new("s")) {
+            println!("cargo:rerun-if-changed={}", path.display());
+        }
+    }
 }

stage1/src/asm/common.s

@@ -0,0 +1,19 @@
+/*
+ * This is the first file to be included in mod.rs,
+ * which exposes its contents to all following files
+ */
+
+	.macro LOCAL name, type=function
+	.type \name , @\type
+\name :
+	.endm
+
+	.macro GLOBL name, type=function
+	.global \name
+	.type \name , %\type
+\name :
+	.endm
+
+	.macro END name
+	.size \name , . - \name
+	.endm

stage1/src/asm/header.s

@@ -0,0 +1,57 @@
+/*
+ * This sits at the very beginning of the stage1 image, which in turn is
+ * located at the beginning of the bussy boot partition.  stage0 always reads
+ * the first 32 K of that partition to 0x0500, validates the magic number and
+ * checksum, and then jumps to the entry point at 0x0510.
+ *
+ * ATTENTION: if you change the structure of this header, you must
+ * also change the (hardcoded) offsets in stage0.s and build.py!
+ */
+
+	.extern _stage1_start	/* stage1.ld */
+	.extern _stage1_end	/* stage1.ld */
+
+	.section .header, "awx"
+	.code16
+
+	/*
+	 * offset 0x00 (loaded at 0x0500)
+	 * stage1 magic number.  stage0 checks this.
+	 */
+GLOBL _stage1_magic, object
+	.word 0xacab
+END _stage1_magic
+
+	/*
+	 * offset 0x02 (loaded at 0x0502)
+	 * Length of the entire stage1 image in bytes, excluding bss.
+	 * Hardcoded during image build.  Must not exceed 32 K.
+	 */
+GLOBL _stage1_len, object
+	.word 0x8000
+END _stage1_len
+
+	/*
+	 * offset 0x04 (loaded at 0x0504)
+	 * CRC32 (polynomial 0x04c11db7) checksum of the entire stage1 image
+	 * as defined by the length field at offset 0x02.  Must be zeroed for
+	 * checksum calculation.  stage0 checks AND CLEARS this.
+	 * Hardcoded during image build.
+	 */
+GLOBL _stage1_csum, object
+	.long 0
+END _stage1_csum
+
+	/*
+	 * offset 0x08 (loaded at 0x0508)
+	 * Reserved; MUST be set to 0.  stage0 ignores this.
+	 */
+	.quad 0
+
+	/*
+	 * offset 0x10 (loaded at 0x0510)
+	 * stage1 entry point.  stage0 jumps here.
+	 */
+GLOBL _start
+1:	jmp	1b
+END _start

stage1/src/asm/mod.rs

@@ -0,0 +1,21 @@
+macro_rules! include_asm {
+    ($name:literal) => {
+        ::core::arch::global_asm!(
+            ::core::concat!(".file \"", $name, "\""), // for better debugging
+            ::core::include_str!($name),
+            ::core::concat!(".file \"", ::core::file!(), "\""),
+            options(raw, att_syntax),
+        );
+    };
+}
+
+// common macros for the other assembly files, keep at the beginning
+include_asm!("common.s");
+
+// stage1 header containing its magic, size, checksum, and entry point
+include_asm!("header.s");
+extern "C" {
+    pub static _stage1_magic: u16;
+    pub static _stage1_len: u16;
+    pub static _stage1_csum: u32;
+}

stage1/src/main.rs

@@ -4,6 +4,8 @@
 use core::arch::asm;
 use core::panic::PanicInfo;
 
+mod asm;
+
 #[no_mangle]
 pub extern "C" fn main() -> ! {
     loop {}