add 32-bit assembly

2 files changed, 21 insertions, 9 deletions

diff --git a/src/boot.s b/src/boot.s
new file mode 100644
index 0000000..2530d18
--- /dev/null
+++ b/src/boot.s
@@ -0,0 +1,17 @@
+.global _start
+.type _start, @function
+
+.code32
+// Entry point. It puts the machine into a consistent state,
+// starts the kernel and then waits forever.
+_start:
+    mov _sstack, %esp  // Setup the stack.
+
+    push %ebx   // Pass multiboot info structure.
+    push %eax   // Pass multiboot magic code.
+    call kmain  // Call the kernel.
+
+    // Halt the CPU.
+    cli
+    hlt
+
diff --git a/src/main.zig b/src/main.zig
index 76bdadf..f3ea424 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -1,9 +1,12 @@
+comptime {
+    asm (@embedFile("boot.s"));
+}
+
 const debug = @import("debugcon.zig");
 
 const ALIGN = 1 << 0;
 const MEMINFO = 1 << 1;
 const MAGIC = 0xE85250D6;
-// const FLAGS = ALIGN | MEMINFO;
 const FLAGS = 0;
 
 const MultibootHeader = extern struct {
@@ -27,14 +30,6 @@ export const multiboot2 align(4) linksection(".multiboot") = MultibootHeader{
     .tag2 = 8,
 };
 
-export fn _start() callconv(.Naked) noreturn {
-    asm volatile (
-        \\ mov _sstack, %rsp
-        \\ mov %rsp, %rbp
-    );
-    asm volatile ("jmp kmain");
-}
-
 var vga = @as([*]volatile u16, @ptrFromInt(0xB8000));
 
 export fn kmain() noreturn {