From 951ef07b9bac01fec7462ca25e0500beeffbf81e Mon Sep 17 00:00:00 2001
From: Sam Tebbs <samuel.tebbs@gmail.com>
Date: Sat, 20 Jun 2020 15:48:55 +0100
Subject: [PATCH] Fix x86 payload passing

---
 src/kernel/arch/x86/boot.zig | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/src/kernel/arch/x86/boot.zig b/src/kernel/arch/x86/boot.zig
index d5ba0b0..8cc075a 100644
--- a/src/kernel/arch/x86/boot.zig
+++ b/src/kernel/arch/x86/boot.zig
@@ -1,4 +1,5 @@
 const constants = @import("constants");
+const multiboot_info = @import("multiboot.zig").multiboot_info_t;
 
 /// The multiboot header
 const MultiBoot = packed struct {
@@ -63,8 +64,9 @@ export var boot_page_directory: [1024]u32 align(4096) linksection(".rodata.boot"
 };
 
 export var kernel_stack: [16 * 1024]u8 align(16) linksection(".bss.stack") = undefined;
+extern var KERNEL_ADDR_OFFSET: *u32;
 
-extern fn kmain() void;
+extern fn kmain(mb_info: *multiboot_info) void;
 
 export fn _start() align(16) linksection(".text.boot") callconv(.Naked) noreturn {
     // Set the page directory to the boot directory
@@ -99,15 +101,14 @@ export fn start_higher_half() callconv(.Naked) noreturn {
     asm volatile (
         \\.extern KERNEL_STACK_END
         \\mov $KERNEL_STACK_END, %%esp
-        \\xor %%ebp, %%ebp
+        \\mov %%esp, %%ebp
     );
 
-    // Push the multiboot header address with virtual offset
-    asm volatile (
-        \\.extern KERNEL_ADDR_OFFSET
-        \\add $KERNEL_ADDR_OFFSET, %%ebx
-        \\push %%ebx
-    );
-    kmain();
+    // Get the multiboot header address and add the virtual offset
+    const mb_info_addr = asm (
+        \\mov %%ebx, %[res]
+        : [res] "=r" (-> usize)
+    ) + @ptrToInt(&KERNEL_ADDR_OFFSET);
+    kmain(@intToPtr(*multiboot_info, mb_info_addr));
     while (true) {}
 }