From 23e0ccf7b5a0ccea545f231d35dbecc00011a9de Mon Sep 17 00:00:00 2001
From: Johannes Stoelp <johannes.stoelp@gmail.com>
Date: Thu, 24 Apr 2025 00:21:02 +0200
Subject: multiboot: add multiboot example kernel

---
 x86-bare-metal/multiboot/kern.zig | 47 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)
 create mode 100644 x86-bare-metal/multiboot/kern.zig

(limited to 'x86-bare-metal/multiboot/kern.zig')

diff --git a/x86-bare-metal/multiboot/kern.zig b/x86-bare-metal/multiboot/kern.zig
new file mode 100644
index 0000000..d8f9c96
--- /dev/null
+++ b/x86-bare-metal/multiboot/kern.zig
@@ -0,0 +1,47 @@
+const fmt = @import("std").fmt;
+const dbg = @import("std").debug;
+
+const vga = @import("vga.zig");
+const mb = @import("mb.zig");
+
+export const mbhdr align(4) linksection(".mbhdr") = mb.HEADER;
+
+var KERNEL_STACK: [32 * 4096]u8 align(16) = undefined;
+
+export fn _start() align(16) linksection(".text.boot") callconv(.naked) noreturn {
+    @setRuntimeSafety(false);
+    asm volatile (
+        \\mov %%eax, %%esp
+        // Push paddr of multiboot info structure on ask (per abi first integer argument to the fn).
+        \\pushl %%ebx
+        \\call kmain
+        \\1: hlt
+        \\jmp 1b
+        :
+        : [top] "{eax}" (@intFromPtr(&KERNEL_STACK) + KERNEL_STACK.len),
+    );
+}
+
+export fn kmain(ebx: u32) void {
+    var con = vga.vga(10, 0).init;
+    con.puts("Booting into kmain()\n\n");
+
+    mb.formatBootinfo(con.writer(), mb.bootinfo(ebx)) catch {};
+
+    dbg.panic("{s}:{}:{s}: done...", .{ @src().file, @src().line, @src().fn_name });
+}
+
+// -- PANIC HANDLER -------------------------------------------------------------
+
+pub const panic = dbg.FullPanic(panicHandler);
+
+fn panicHandler(msg: []const u8, first_trace_addr: ?usize) noreturn {
+    _ = first_trace_addr;
+
+    var con = vga.vga(11, 0).init;
+    fmt.format(con.writer(), "\nPANIC: {s}\n", .{msg}) catch {};
+
+    while (true) {
+        asm volatile ("hlt");
+    }
+}
-- 
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