From c81b85875734d5c84809309e3c1c3bcd1457eb8c Mon Sep 17 00:00:00 2001
From: belliash <belliash@codingworkshop.eu.org>
Date: Mon, 23 Jan 2023 19:59:54 +0100
Subject: [PATCH] Implement HlReadGSQuadWord() intrinsic

---
 sdk/xtdk/amd64/hlfuncs.h    |  4 ++++
 xtoskrnl/hl/amd64/cpufunc.c | 21 +++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/sdk/xtdk/amd64/hlfuncs.h b/sdk/xtdk/amd64/hlfuncs.h
index c980ee2..947382a 100644
--- a/sdk/xtdk/amd64/hlfuncs.h
+++ b/sdk/xtdk/amd64/hlfuncs.h
@@ -67,6 +67,10 @@ XTCDECL
 ULONG_PTR
 HlReadControlRegister(IN USHORT ControlRegister);
 
+XTCDECL
+ULONGLONG
+HlReadGSQuadWord(ULONG Offset);
+
 XTCDECL
 ULONGLONG
 HlReadModelSpecificRegister(IN ULONG Register);
diff --git a/xtoskrnl/hl/amd64/cpufunc.c b/xtoskrnl/hl/amd64/cpufunc.c
index 8c4cf78..ae68d3a 100644
--- a/xtoskrnl/hl/amd64/cpufunc.c
+++ b/xtoskrnl/hl/amd64/cpufunc.c
@@ -318,6 +318,27 @@ HlReadControlRegister(IN USHORT ControlRegister)
     return Value;
 }
 
+/**
+ * Reads quadword from a memory location specified by an offset relative to the beginning of the GS segment.
+ *
+ * @param Offset
+ *        Specifies the offset from the beginning of GS segment.
+ *
+ * @return Returns the value read from the specified memory location relative to GS segment.
+ *
+ * @since XT 1.0
+ */
+XTCDECL
+ULONGLONG
+HlReadGSQuadWord(ULONG Offset)
+{
+    ULONGLONG Value;
+
+    /* Read quadword from GS segment */
+    asm volatile("movq %%gs:%a[Offset], %q[Value]" : [Value] "=r" (Value) : [Offset] "ir" (Offset));
+    return Value;
+}
+
 /**
  * Reads a 64-bit value from the requested Model Specific Register (MSR).
  *