From b8a0024ee71a64ec0e87a1e2d0c0c7280dc954e6 Mon Sep 17 00:00:00 2001
From: Fabian Imhof <fabian.imhof@ost.ch>
Date: Thu, 13 Mar 2025 09:36:00 +0000
Subject: create GDT and fix segment descriptor bit order

---
 arch/x86_64/src/kernel/main.cpp | 50 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

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

diff --git a/arch/x86_64/src/kernel/main.cpp b/arch/x86_64/src/kernel/main.cpp
index 472aed5..d3938ed 100644
--- a/arch/x86_64/src/kernel/main.cpp
+++ b/arch/x86_64/src/kernel/main.cpp
@@ -1,9 +1,11 @@
 #include "arch/kernel/main.hpp"
 
+#include "arch/context_switching/descriptor_table/segment_descriptor.hpp"
 #include "arch/memory/heap/bump_allocator.hpp"
 #include "arch/memory/heap/global_heap_allocator.hpp"
 #include "arch/memory/main.hpp"
 #include "arch/memory/multiboot/reader.hpp"
+#include "arch/stl/vector.hpp"
 #include "arch/video/vga/text.hpp"
 
 namespace teachos::arch::kernel
@@ -57,5 +59,53 @@ namespace teachos::arch::kernel
     memory::heap::global_heap_allocator::register_heap_allocator(memory::heap::heap_allocator_type::LINKED_LIST);
 
     heap_test();
+
+    using context_switching::descriptor_table::access_byte;
+    using context_switching::descriptor_table::gdt_flags;
+    using context_switching::descriptor_table::segment_descriptor;
+    using context_switching::descriptor_table::segment_descriptor_type;
+    using context_switching::descriptor_table::type_field;
+
+    segment_descriptor null_segment{0};
+
+    // Kernel space code segment
+    access_byte kernel_code_access_byte{access_byte::PRESENT | access_byte::ACCESS_LEVEL_KERNEL |
+                                            access_byte::CODE_OR_DATA_SEGMENT,
+                                        type_field::CODE_SEGMENT | type_field::READABLE};
+    gdt_flags kernel_code_gdt_flags{gdt_flags::GRANULARITY | gdt_flags::LENGTH};
+    segment_descriptor kernel_code_segment{kernel_code_access_byte, kernel_code_gdt_flags, 0, 0xFFFFF};
+
+    // Kernel space data segment
+    access_byte kernel_data_access_byte{access_byte::PRESENT | access_byte::ACCESS_LEVEL_KERNEL |
+                                            access_byte::CODE_OR_DATA_SEGMENT,
+                                        type_field::WRITABLE};
+    gdt_flags kernel_data_gdt_flags{gdt_flags::GRANULARITY | gdt_flags::UPPER_BOUND};
+    segment_descriptor kernel_data_segment{kernel_data_access_byte, kernel_data_gdt_flags, 0, 0xFFFFF};
+
+    // User space code segment
+    access_byte user_code_access_byte{access_byte::PRESENT | access_byte::ACCESS_LEVEL_USER |
+                                          access_byte::CODE_OR_DATA_SEGMENT,
+                                      type_field::CODE_SEGMENT | type_field::READABLE};
+    gdt_flags user_code_gdt_flags{gdt_flags::GRANULARITY | gdt_flags::LENGTH};
+    segment_descriptor user_code_segment{user_code_access_byte, user_code_gdt_flags, 0, 0xFFFFF};
+
+    // User space data segment
+    access_byte user_data_access_byte{access_byte::PRESENT | access_byte::ACCESS_LEVEL_USER |
+                                          access_byte::CODE_OR_DATA_SEGMENT,
+                                      type_field::WRITABLE};
+    gdt_flags user_data_gdt_flags{gdt_flags::GRANULARITY | gdt_flags::UPPER_BOUND};
+    segment_descriptor user_data_segment{user_data_access_byte, user_data_gdt_flags, 0, 0xFFFFF};
+
+    stl::vector<segment_descriptor> global_descriptor_table{null_segment, kernel_code_segment, kernel_data_segment,
+                                                            user_code_segment, user_data_segment};
+
+    decltype(auto) x = global_descriptor_table.at(1);
+    if (global_descriptor_table.size() == 0)
+    {
+    }
+    if (x.get_segment_type() == segment_descriptor_type::CODE_SEGMENT)
+    {
+    }
+    video::vga::text::write("GDT FILLED", video::vga::text::common_attributes::green_on_black);
   }
 }  // namespace teachos::arch::kernel
-- 
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