From 6cdb66cbb3031f5b27266f5a11bb13d9da296a50 Mon Sep 17 00:00:00 2001
From: Aiken Harris <harraiken91@gmail.com>
Date: Sun, 15 Mar 2026 00:33:09 +0100
Subject: [PATCH] Ensure SS and ESP are saved in trap frame

---
 xtoskrnl/ar/i686/archsup.S         | 11 ++++++++++-
 xtoskrnl/includes/ar/i686/asmsup.h |  4 +++-
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/xtoskrnl/ar/i686/archsup.S b/xtoskrnl/ar/i686/archsup.S
index f1af307..4e73bc1 100644
--- a/xtoskrnl/ar/i686/archsup.S
+++ b/xtoskrnl/ar/i686/archsup.S
@@ -75,12 +75,20 @@ _ArTrap\Vector:
     /* Test previous mode and swap GS if needed */
     movl $0, TrapPreviousMode(%ebp)
     mov %cs, %ax
-    and $1, %al
+    and $3, %al
     mov %al, TrapPreviousMode(%ebp)
     jz KernelMode$\Vector
     swapgs
+    jmp UserMode$\Vector
 
 KernelMode$\Vector:
+    /* Save kernel stack pointer (SS:ESP) as CPU did not push them */
+    movl %ss, %eax
+    mov %eax, TrapSegSs(%ebp)
+    lea TrapEsp(%ebp), %eax
+    mov %eax, TrapEsp(%ebp)
+
+UserMode$\Vector:
     /* Push Frame Pointer, clear direction flag and pass to trap dispatcher */
     push %esp
     cld
@@ -100,6 +108,7 @@ KernelModeReturn$\Vector:
     mov TrapSegDs(%ebp), %ds
     mov TrapSegEs(%ebp), %es
     mov TrapSegFs(%ebp), %fs
+    mov TrapSegGs(%ebp), %gs
 
     /* Free stack space */
     add $(TRAP_FRAME_SIZE - TRAP_REGISTERS_SIZE), %esp
diff --git a/xtoskrnl/includes/ar/i686/asmsup.h b/xtoskrnl/includes/ar/i686/asmsup.h
index 7eab0f5..5150fb9 100644
--- a/xtoskrnl/includes/ar/i686/asmsup.h
+++ b/xtoskrnl/includes/ar/i686/asmsup.h
@@ -24,9 +24,11 @@
 #define TrapSegEs                               38
 #define TrapSegFs                               40
 #define TrapSegGs                               42
+#define TrapEsp                                 92
+#define TrapSegSs                               96
 
 /* KTRAP_FRAME length related definitions */
 #define TRAP_FRAME_SIZE                         100
 #define TRAP_REGISTERS_SIZE                     56
 
-#endif /* __XTOSKRNL_AMD64_ASMSUP_H */
+#endif /* __XTOSKRNL_I686_ASMSUP_H */