From a32e18b2379ff82da118bba30694627f259f497f Mon Sep 17 00:00:00 2001
From: belliash <belliash@codingworkshop.eu.org>
Date: Tue, 7 Feb 2023 23:19:22 +0100
Subject: [PATCH] Implement ArReadFSDualWord() routine

---
 sdk/xtdk/i686/arfuncs.h    |  4 ++++
 xtoskrnl/ar/i686/cpufunc.c | 21 +++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/sdk/xtdk/i686/arfuncs.h b/sdk/xtdk/i686/arfuncs.h
index 7e9d976..603240d 100644
--- a/sdk/xtdk/i686/arfuncs.h
+++ b/sdk/xtdk/i686/arfuncs.h
@@ -57,6 +57,10 @@ XTCDECL
 ULONG_PTR
 ArReadControlRegister(IN USHORT ControlRegister);
 
+XTCDECL
+ULONG
+ArReadFSDualWord(ULONG Offset);
+
 XTCDECL
 ULONGLONG
 ArReadModelSpecificRegister(IN ULONG Register);
diff --git a/xtoskrnl/ar/i686/cpufunc.c b/xtoskrnl/ar/i686/cpufunc.c
index b2d3312..9afc616 100644
--- a/xtoskrnl/ar/i686/cpufunc.c
+++ b/xtoskrnl/ar/i686/cpufunc.c
@@ -270,6 +270,27 @@ ArReadControlRegister(IN USHORT ControlRegister)
     return Value;
 }
 
+/**
+ * Reads dualword from a memory location specified by an offset relative to the beginning of the FS segment.
+ *
+ * @param Offset
+ *        Specifies the offset from the beginning of FS segment.
+ *
+ * @return Returns the value read from the specified memory location relative to FS segment.
+ *
+ * @since XT 1.0
+ */
+XTCDECL
+ULONG
+ArReadFSDualWord(ULONG Offset)
+{
+    ULONG Value;
+    asm volatile("movl %%fs:%a[Offset], %k[Value]"
+                 : [Value] "=r" (Value)
+                 : [Offset] "ir" (Offset));
+    return Value;
+}
+
 /**
  * Reads a 64-bit value from the requested Model Specific Register (MSR).
  *