From 2b8e6e7e10f084a9a9ba5c0b79a041f4d1ac459b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Matteo=20Gm=C3=BCr?= <matteo.gmuer1@ost.ch>
Date: Sat, 15 Mar 2025 11:29:26 +0000
Subject: implement loading of gdtr register

---
 arch/x86_64/src/kernel/cpu/lgdt.cpp | 13 ++++++++-----
 arch/x86_64/src/kernel/cpu/ss.cpp   |  8 ++++----
 2 files changed, 12 insertions(+), 9 deletions(-)

(limited to 'arch/x86_64/src/kernel/cpu')

diff --git a/arch/x86_64/src/kernel/cpu/lgdt.cpp b/arch/x86_64/src/kernel/cpu/lgdt.cpp
index 70a48dd..386914f 100644
--- a/arch/x86_64/src/kernel/cpu/lgdt.cpp
+++ b/arch/x86_64/src/kernel/cpu/lgdt.cpp
@@ -4,14 +4,17 @@
 
 namespace teachos::arch::kernel::cpu
 {
+  auto store_global_descriptor_table() -> context_switching::descriptor_table::global_descriptor_table_pointer
+  {
+    context_switching::descriptor_table::global_descriptor_table_pointer current_value{};
+    asm("sgdt %[output]" : [output] "=m"(current_value));
+    return current_value;
+  }
+
   auto
   load_global_descriptor_table(context_switching::descriptor_table::global_descriptor_table_pointer const & gdt_pointer)
       -> void
   {
-    // TODO: build lgdt argument from global_descriptor_table_pointer (don't know how yet)
-    // asm volatile("lgdt (%0)" : : "r"(gdt_pointer));
-    if (gdt_pointer.table_length)
-    {
-    }
+    asm volatile("lgdt %[input]" : /* no output from call */ : [input] "m"(gdt_pointer));
   }
 }  // namespace teachos::arch::kernel::cpu
diff --git a/arch/x86_64/src/kernel/cpu/ss.cpp b/arch/x86_64/src/kernel/cpu/ss.cpp
index 9c8dd61..1f28e7f 100644
--- a/arch/x86_64/src/kernel/cpu/ss.cpp
+++ b/arch/x86_64/src/kernel/cpu/ss.cpp
@@ -19,15 +19,15 @@ namespace teachos::arch::kernel::cpu
 
   auto read_ss() -> uint16_t
   {
-    uint16_t ss;
-    asm volatile("mov %%ss, %0" : "=r"(ss));
-    return ss;
+    uint16_t segment_selector;
+    asm volatile("mov %%ss, %[output]" : [output] "=r"(segment_selector));
+    return segment_selector;
   }
 
   auto write_ss(segment_selector selector) -> void
   {
     uint16_t ss = selector.to_uint16();
-    asm volatile("mov %0, %%ss" ::"r"(ss));
+    asm volatile("mov %[input], %%ss" : /* no output from call */ : [input] "r"(ss));
   }
 
 }  // namespace teachos::arch::kernel::cpu
\ No newline at end of file
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