From d88f9f0a15d8a6bd1c3dc83465738b662bf2a8e5 Mon Sep 17 00:00:00 2001
From: Aiken Harris <harraiken91@gmail.com>
Date: Wed, 1 Apr 2026 11:18:28 +0200
Subject: [PATCH] Remove erroneous swapgs and implement proper segment setting

---
 xtoskrnl/ar/i686/archsup.S         | 16 ++++++++++++----
 xtoskrnl/includes/ar/i686/asmsup.h |  7 +++++++
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/xtoskrnl/ar/i686/archsup.S b/xtoskrnl/ar/i686/archsup.S
index dcd8817..7d02b61 100644
--- a/xtoskrnl/ar/i686/archsup.S
+++ b/xtoskrnl/ar/i686/archsup.S
@@ -109,13 +109,22 @@ _Ar\Type\Vector\()Start:
         mov %cr2, %eax
         mov %eax, TrapCr2(%ebp)
 
-        /* Test previous mode and swap GS if needed */
+        /* Test previous mode */
         movl $0, TrapPreviousMode(%ebp)
         mov TrapSegCs(%ebp), %ax
         and $3, %al
         mov %al, TrapPreviousMode(%ebp)
         jz KernelMode\Type\Vector
-        swapgs
+
+        /* Load Kernel PB selector into FS */
+        mov $KGDT_R0_PB, %ax
+        mov %ax, %fs
+
+        /* Set sane data segment selectors */
+        mov $(KGDT_R3_DATA | RPL_MASK), %ax
+        mov %ax, %ds
+        mov %ax, %es
+
         jmp UserMode\Type\Vector
 
 KernelMode\Type\Vector:
@@ -141,11 +150,10 @@ UserMode\Type\Vector:
         /* Clean up the stack */
         add $4, %esp
 
-        /* Test previous mode and swapgs if needed */
+        /* Test previous mode and disable interrupts before user mode return */
         testb $1, TrapPreviousMode(%ebp)
         jz KernelModeReturn\Type\Vector
         cli
-        swapgs
 
 KernelModeReturn\Type\Vector:
         /* Restore segment selectors */
diff --git a/xtoskrnl/includes/ar/i686/asmsup.h b/xtoskrnl/includes/ar/i686/asmsup.h
index 6b228f2..5eb490b 100644
--- a/xtoskrnl/includes/ar/i686/asmsup.h
+++ b/xtoskrnl/includes/ar/i686/asmsup.h
@@ -10,6 +10,13 @@
 #define __XTOSKRNL_I686_ASMSUP_H
 
 
+/* Selector masks */
+#define RPL_MASK                                0x0003
+
+/* GDT selectors */
+#define KGDT_R3_DATA                            0x0020
+#define KGDT_R0_PB                              0x0030
+
 /* KTRAP_FRAME structure offsets */
 #define TrapPreviousMode                        0
 #define TrapCr2                                 4