[Kernel] Compile an AP bootstrap program and include it in the boot i…

…mage

ap_bootstrap.s.x86_64.arch_specific

@@ -1,18 +1,25 @@
 [bits 16]
-
-[section .ap_bootstrap_section]
+[org 0x8000]
 
 [global ap_entry]
 ap_entry:
+    jmp $ap_boot
+
+; PT: This is placeholder memory that will be overwritten to contain the 'parameters' passed to the AP
+align 8
+param1: dd 0
+param2: dd 0
+
+ap_boot:
     cli
-    xor ax, ax
-    mov cs, ax
-    mov dx, ax
-    mov ss, ax
-    mov sp, 0x80
-    mov al, 0xff
+    ; PT: OSDev wiki seems to suggest clearing DF, but I'm not sure why
+    cld
+
+    ; Set some debug register values and write to memory to ensure this code is running
+    mov al, 0x7c
+    mov bl, [$param1]
+    mov cl, [$param2]
     mov [0x2000], al
 
-    jmp $
 .loop:
     jmp $.loop

scripts/build_os_image.py

@@ -64,6 +64,10 @@ def build_iso() -> Path:
     if not initrd_path.exists():
         raise ValueError(f"initrd missing: {initrd_path}")
 
+    ap_bootstrap_path = _REPO_ROOT / ".compiled_ap_bootstrap"
+    if not ap_bootstrap_path.exists():
+        raise ValueError(f"AP bootstrap missing: {ap_bootstrap_path}")
+
     run_and_check(["dd", "if=/dev/zero", f"of={image_name.as_posix()}", "bs=512", "count=262144"])
 
     with _get_mounted_iso(image_name) as mount_point:
@@ -75,6 +79,7 @@ def build_iso() -> Path:
         run_and_check(["mcopy", "-i", image_name.as_posix(), kernel_binary_path.as_posix(), "::/EFI/AXLE/KERNEL.ELF"])
         run_and_check(["mcopy", "-i", image_name.as_posix(), fs_server_path.as_posix(), "::/EFI/AXLE/FS_SERVER.ELF"])
         run_and_check(["mcopy", "-i", image_name.as_posix(), initrd_path.as_posix(), "::/EFI/AXLE/INITRD.IMG"])
+        run_and_check(["mcopy", "-i", image_name.as_posix(), ap_bootstrap_path.as_posix(), "::/EFI/AXLE/AP_BOOTSTRAP.BIN"])
 
     return image_name
 
@@ -167,6 +172,10 @@ def main():
     # Build the Rust kernel libraries
     build_kernel_rust_libs()
 
+    # Build the AP bootstrap, which needs to be outside the kernel proper
+    # TODO(PT): Render this based on the target architecture
+    run_and_check(["nasm", "-f", "bin", (_REPO_ROOT / "ap_bootstrap.s.x86_64.arch_specific").as_posix(), "-o", (_REPO_ROOT / ".compiled_ap_bootstrap").as_posix()])
+
     # Build the C and assembly portions of the kernel, and link with the Rust libraries
     run_and_check(["make"])