Debug and adjust load task register assembly call. WIP

3 files changed, 27 insertions, 25 deletions

diff --git a/arch/x86_64/src/context_switching/descriptor_table/global_descriptor_table.cpp b/arch/x86_64/src/context_switching/descriptor_table/global_descriptor_table.cpp
index 21a76e8..b338d9d 100644
--- a/arch/x86_64/src/context_switching/descriptor_table/global_descriptor_table.cpp
+++ b/arch/x86_64/src/context_switching/descriptor_table/global_descriptor_table.cpp
@@ -34,44 +34,41 @@ namespace teachos::arch::context_switching::descriptor_table
       access_level_bitset |= access_byte::WRITABLE;
     }
 
-    uint64_t base = 0x0;
-    std::bitset<20U> limit{0xFFFFF};
-    access_byte access_byte{access_level_bitset};
-    gdt_flags gdt_flags{gdt_flags_bitset, limit};
-    segment_descriptor code_segment{access_byte, gdt_flags, base, limit};
-
+    uint64_t const base = 0x0;
+    std::bitset<20U> const limit{0xFFFFF};
+    access_byte const access_byte{access_level_bitset};
+    gdt_flags const gdt_flags{gdt_flags_bitset, limit};
+    segment_descriptor const code_segment{access_byte, gdt_flags, base, limit};
     return code_segment;
   }
 
   auto create_global_descriptor_table() -> global_descriptor_table
   {
-    segment_descriptor null_segment{0};
-    segment_descriptor kernel_code_segment =
+    segment_descriptor const null_segment{0};
+    segment_descriptor const kernel_code_segment =
         create_segment_descriptor(segment_descriptor_type::CODE_SEGMENT, access_level::KERNEL);
-    segment_descriptor kernel_data_segment =
+    segment_descriptor const kernel_data_segment =
         create_segment_descriptor(segment_descriptor_type::DATA_SEGMENT, access_level::KERNEL);
-    segment_descriptor user_code_segment =
+    segment_descriptor const user_code_segment =
         create_segment_descriptor(segment_descriptor_type::CODE_SEGMENT, access_level::USER);
-    segment_descriptor user_data_segment =
+    segment_descriptor const user_data_segment =
         create_segment_descriptor(segment_descriptor_type::DATA_SEGMENT, access_level::USER);
     // Task State Segment needs to be kept alive
     static auto tss = new task_state_segment();
-    segment_descriptor tss_descriptor = create_task_state_segment_descriptor(tss);
+    segment_descriptor const tss_descriptor = create_task_state_segment_descriptor(tss);
 
-    global_descriptor_table global_descriptor_table{null_segment,      kernel_code_segment, kernel_data_segment,
-                                                    user_code_segment, user_data_segment,   tss_descriptor};
+    global_descriptor_table const global_descriptor_table{null_segment,      kernel_code_segment, kernel_data_segment,
+                                                          user_code_segment, user_data_segment,   tss_descriptor};
     return global_descriptor_table;
   }
 
   auto create_task_state_segment_descriptor(task_state_segment * tss) -> segment_descriptor
   {
-    std::bitset<20U> limit{0xFFFFF};
-    access_byte tss_access_byte{access_byte::PRESENT | access_byte::ACCESS_LEVEL_KERNEL |
-                                access_byte::TASK_STATE_SEGMENT_AVAILABLE};
-    gdt_flags tss_gdt_flags{0U, limit};
-    uint64_t tss_address = reinterpret_cast<uint64_t>(tss);
     constexpr uint64_t TSS_LIMIT = sizeof(task_state_segment) - 1;
-    segment_descriptor tss_descriptor{tss_access_byte, tss_gdt_flags, tss_address, TSS_LIMIT};
+    access_byte const tss_access_byte{access_byte::PRESENT | access_byte::ACCESS_LEVEL_KERNEL |
+                                      access_byte::TASK_STATE_SEGMENT_AVAILABLE};
+    gdt_flags const tss_gdt_flags{0U, TSS_LIMIT};
+    segment_descriptor const tss_descriptor{tss_access_byte, tss_gdt_flags, reinterpret_cast<uint64_t>(tss), TSS_LIMIT};
     return tss_descriptor;
   }
 
@@ -80,11 +77,10 @@ namespace teachos::arch::context_switching::descriptor_table
     // Global Descriptor Table needs to be kept alive
     static auto gdt = create_global_descriptor_table();
 
-    // Load GDT into GDTR
     global_descriptor_table_pointer gdt_pointer{static_cast<uint16_t>(gdt.size() - 1), &gdt};
     kernel::cpu::load_global_descriptor_table(gdt_pointer);
 
-    auto stored_gdt_pointer = kernel::cpu::store_global_descriptor_table();
+    auto const stored_gdt_pointer = kernel::cpu::store_global_descriptor_table();
     arch::exception_handling::assert(
         gdt_pointer == stored_gdt_pointer,
         "[Global Descriptor Table] Loaded GDTR value is not the same as the stored value.");
@@ -93,7 +89,7 @@ namespace teachos::arch::context_switching::descriptor_table
     uint16_t const tss_selector = (gdt.size() - 1) * sizeof(segment_descriptor);
     kernel::cpu::load_task_register(tss_selector);
 
-    auto stored_task_register = kernel::cpu::store_task_register();
+    auto const stored_task_register = kernel::cpu::store_task_register();
     arch::exception_handling::assert(tss_selector == stored_task_register,
                                      "[Global Descriptor Table] Loaded TR value is not the same as the stored value.");
     return gdt;
diff --git a/arch/x86_64/src/context_switching/descriptor_table/segment_descriptor.cpp b/arch/x86_64/src/context_switching/descriptor_table/segment_descriptor.cpp
index 3e93823..2385c58 100644
--- a/arch/x86_64/src/context_switching/descriptor_table/segment_descriptor.cpp
+++ b/arch/x86_64/src/context_switching/descriptor_table/segment_descriptor.cpp
@@ -15,7 +15,7 @@ namespace teachos::arch::context_switching::descriptor_table
   segment_descriptor::segment_descriptor(access_byte access_byte, gdt_flags flags, uint64_t base,
                                          std::bitset<20U> limit)
       : _limit_1(limit.to_ulong())
-      , _base_1((base << 40U) >> 40U)
+      , _base_1(base)
       , _access(access_byte)
       , _flag(flags)
       , _base_2(base >> 24U)
diff --git a/arch/x86_64/src/kernel/cpu/tr.cpp b/arch/x86_64/src/kernel/cpu/tr.cpp
index d0e037f..e281189 100644
--- a/arch/x86_64/src/kernel/cpu/tr.cpp
+++ b/arch/x86_64/src/kernel/cpu/tr.cpp
@@ -11,6 +11,12 @@ namespace teachos::arch::kernel::cpu
 
   auto load_task_register(uint16_t gdt_offset) -> void
   {
-    asm volatile("ltr %[input]" : /* no output from call */ : [input] "r"(gdt_offset));
+    // asm volatile("ltr %[input]" : /* no output from call */ : [input] "R"(gdt_offset));
+    //  https://www.scs.stanford.edu/05au-cs240c/lab/i386/s07_03.htm
+    asm volatile("mov %[input], %%ax\n"
+                 "ltr %%ax\n"
+                 : /* no output from call */
+                 : [input] "r"(gdt_offset)
+                 : "ax");
   }
 }  // namespace teachos::arch::kernel::cpu