From 6677ab1ccd2c9f677782ff131889dab890fe53b0 Mon Sep 17 00:00:00 2001
From: Jean-Baptiste Boric <jblbeurope@gmail.com>
Date: Mon, 18 Jan 2021 20:24:25 +0100
Subject: Boot: Fix undefined Multiboot behaviors

Both ESP and GDTR are left undefined by the Multiboot specification and
OS images must not rely on these values to be valid. Fix the undefined
behaviors so that booting with PXELINUX does not triple-fault the CPU.
---
 Kernel/Arch/i386/Boot/boot.S | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

(limited to 'Kernel/Arch/i386/Boot')

diff --git a/Kernel/Arch/i386/Boot/boot.S b/Kernel/Arch/i386/Boot/boot.S
index 4fce416868..d0ced81de4 100644
--- a/Kernel/Arch/i386/Boot/boot.S
+++ b/Kernel/Arch/i386/Boot/boot.S
@@ -194,10 +194,13 @@ start:
     orl $0x80000000, %eax
     movl %eax, %cr0
 
+    /* set up stack */
+    mov $stack_top, %esp
+    and $-16, %esp
+
     /* jmp to an address above the 3GB mark */
-    push %cs
-    push $1f 
-    retf
+    movl $1f,%eax
+    jmp *%eax
 1:
     movl %cr3, %eax
     movl %eax, %cr3
@@ -212,10 +215,7 @@ start:
     addl $8, %edi
     loop 1b
 
-    /* set up initial stack and jump into C++ land */
-    mov $stack_top, %esp
-    and $-16, %esp
-
+    /* jump into C++ land */
     addl $0xc0000000, %ebx
     movl %ebx, multiboot_info_ptr
 
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