From 2e4cbd473ff3bb7ac7371af39becf830b4fb753b Mon Sep 17 00:00:00 2001
From: Fabian Imhof <fabian.imhof@ost.ch>
Date: Thu, 13 Mar 2025 14:05:45 +0000
Subject: IN_PROGRESS implement gdt initialization

---
 arch/x86_64/src/kernel/cpu/msr.cpp | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)
 create mode 100644 arch/x86_64/src/kernel/cpu/msr.cpp

(limited to 'arch/x86_64/src/kernel/cpu/msr.cpp')

diff --git a/arch/x86_64/src/kernel/cpu/msr.cpp b/arch/x86_64/src/kernel/cpu/msr.cpp
new file mode 100644
index 0000000..082bca9
--- /dev/null
+++ b/arch/x86_64/src/kernel/cpu/msr.cpp
@@ -0,0 +1,31 @@
+#include "arch/kernel/cpu/msr.hpp"
+
+namespace teachos::arch::memory::cpu
+{
+  namespace
+  {
+    auto constexpr IA32_EFER_ADDRESS = 0xC0000080;
+  }
+
+  auto read_msr(uint32_t msr) -> uint64_t
+  {
+    uint32_t low, high;
+    asm volatile("rdmsr" : "=a"(low), "=d"(high) : "c"(msr));
+    return (static_cast<uint64_t>(high) << 32) | low;
+  }
+
+  auto write_msr(uint32_t msr, uint64_t value) -> void
+  {
+    uint32_t low = value & 0xFFFFFFFF;
+    uint32_t high = value >> 32;
+    asm volatile("wrmsr"
+                 : /* no output from call */
+                 : "c"(msr), "a"(low), "d"(high));
+  }
+
+  auto set_efer_bit(efer_flags flag) -> void
+  {
+    auto const efer = read_msr(IA32_EFER_ADDRESS);
+    write_msr(IA32_EFER_ADDRESS, static_cast<std::underlying_type<efer_flags>::type>(flag) | efer);
+  }
+}  // namespace teachos::arch::memory::cpu
-- 
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