Fix size of segment descriptor using bit fields and struct packing

5 files changed, 35 insertions, 51 deletions

diff --git a/arch/x86_64/src/context_switching/descriptor_table/access_byte.cpp b/arch/x86_64/src/context_switching/descriptor_table/access_byte.cpp
index 4e5459f..6b54451 100644
--- a/arch/x86_64/src/context_switching/descriptor_table/access_byte.cpp
+++ b/arch/x86_64/src/context_switching/descriptor_table/access_byte.cpp
@@ -2,14 +2,14 @@
 
 namespace teachos::arch::context_switching::descriptor_table
 {
-  access_byte::access_byte(uint8_t flags, uint8_t type_field)
+  access_byte::access_byte(uint8_t flags)
       : _flags(flags)
-      , _type(type_field)
   {
     // Nothing to do.
   }
 
-  auto access_byte::contains_flags(std::bitset<4U> other) const -> bool { return (_flags & other) == other; }
-
-  auto access_byte::get_type_field() const -> type_field { return _type; }
+  auto access_byte::contains_flags(std::bitset<8U> other) const -> bool
+  {
+    return (std::bitset<8U>{_flags} & other) == other;
+  }
 }  // namespace teachos::arch::context_switching::descriptor_table
diff --git a/arch/x86_64/src/context_switching/descriptor_table/gdt_flags.cpp b/arch/x86_64/src/context_switching/descriptor_table/gdt_flags.cpp
index 65f2e90..9e95182 100644
--- a/arch/x86_64/src/context_switching/descriptor_table/gdt_flags.cpp
+++ b/arch/x86_64/src/context_switching/descriptor_table/gdt_flags.cpp
@@ -1,14 +1,18 @@
 #include "arch/context_switching/descriptor_table/gdt_flags.hpp"
 
-#include "arch/exception_handling/assert.hpp"
-
 namespace teachos::arch::context_switching::descriptor_table
 {
-  gdt_flags::gdt_flags(uint8_t flags)
-      : _flags(flags)
+  gdt_flags::gdt_flags(uint8_t flags, std::bitset<20U> limit)
+      : _limit_2(limit.to_ulong() >> 16U)
+      , _flags(flags)
   {
     // Nothing to do.
   }
 
-  auto gdt_flags::contains_flags(std::bitset<4U> other) const -> bool { return (_flags & other) == other; }
+  auto gdt_flags::contains_flags(std::bitset<4U> other) const -> bool
+  {
+    return (std::bitset<4U>{_flags} & other) == other;
+  }
+
+  auto descriptor_table::gdt_flags::get_limit() const -> std::bitset<4U> { return std::bitset<4U>{_limit_2}; }
 }  // namespace teachos::arch::context_switching::descriptor_table
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 f4ea61b..cbd230b 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
@@ -10,33 +10,32 @@ namespace teachos::arch::context_switching::descriptor_table
   {
     segment_descriptor null_segment{0};
 
+    std::bitset<20U> limit{0xFFFFF};
     // 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};
+                                        access_byte::CODE_OR_DATA_SEGMENT | access_byte::CODE_SEGMENT |
+                                        access_byte::READABLE};
+    gdt_flags kernel_code_gdt_flags{gdt_flags::GRANULARITY | gdt_flags::LENGTH, limit};
+    segment_descriptor kernel_code_segment{kernel_code_access_byte, kernel_code_gdt_flags, 0, limit};
 
     // 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};
+                                        access_byte::CODE_OR_DATA_SEGMENT | access_byte::WRITABLE};
+    gdt_flags kernel_data_gdt_flags{gdt_flags::GRANULARITY | gdt_flags::UPPER_BOUND, limit};
+    segment_descriptor kernel_data_segment{kernel_data_access_byte, kernel_data_gdt_flags, 0, limit};
 
     // 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};
+                                      access_byte::CODE_OR_DATA_SEGMENT | access_byte::CODE_SEGMENT |
+                                      access_byte::READABLE};
+    gdt_flags user_code_gdt_flags{gdt_flags::GRANULARITY | gdt_flags::LENGTH, limit};
+    segment_descriptor user_code_segment{user_code_access_byte, user_code_gdt_flags, 0, limit};
 
     // 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};
+                                      access_byte::CODE_OR_DATA_SEGMENT | access_byte::WRITABLE};
+    gdt_flags user_data_gdt_flags{gdt_flags::GRANULARITY | gdt_flags::UPPER_BOUND, limit};
+    segment_descriptor user_data_segment{user_data_access_byte, user_data_gdt_flags, 0, limit};
 
     stl::vector<segment_descriptor> global_descriptor_table{null_segment, kernel_code_segment, kernel_data_segment,
                                                             user_code_segment, user_data_segment};
@@ -46,7 +45,7 @@ namespace teachos::arch::context_switching::descriptor_table
   auto initialize_global_descriptor_table() -> global_descriptor_table
   {
     decltype(auto) gdt = create_global_descriptor_table();
-    global_descriptor_table_pointer gdt_pointer{gdt.size() - 1, &gdt};
+    global_descriptor_table_pointer gdt_pointer{static_cast<uint16_t>(gdt.size() - 1), &gdt};
     kernel::cpu::load_global_descriptor_table(gdt_pointer);
     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 a743ad2..c1a46a6 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
@@ -5,9 +5,8 @@ namespace teachos::arch::context_switching::descriptor_table
   segment_descriptor::segment_descriptor(uint128_t flags)
       : _limit_1(flags << 112U)
       , _base_1((flags >> 16U) << 88U)
-      , _access((flags >> 44U) << 80U, (flags >> 40U) << 84U)
-      , _limit_2((flags >> 48U) << 72U)
-      , _flag((flags >> 52U) << 72U)
+      , _access((flags >> 40U) << 80U)
+      , _flag((flags >> 52U) << 72U, (flags >> 48U) << 72U)
       , _base_2((flags >> 56U) << 32U)
       , _reserved(flags >> 96U)
   {
@@ -16,10 +15,9 @@ 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() << 4U) >> 16U)
+      : _limit_1(limit.to_ulong())
       , _base_1((base << 40U) >> 40U)
       , _access(access_byte)
-      , _limit_2(limit.to_ulong() >> 16U)
       , _flag(flags)
       , _base_2(base >> 24U)
       , _reserved(0U)
@@ -33,12 +31,7 @@ namespace teachos::arch::context_switching::descriptor_table
     {
       return segment_descriptor_type::SYSTEM_SEGMENT;
     }
-
-    if (_access.get_type_field().contains_flags(type_field::CODE_SEGMENT))
-    {
-      return segment_descriptor_type::CODE_SEGMENT;
-    }
-
-    return segment_descriptor_type::DATA_SEGMENT;
+    return _access.contains_flags(access_byte::CODE_SEGMENT) ? segment_descriptor_type::CODE_SEGMENT
+                                                             : segment_descriptor_type::DATA_SEGMENT;
   }
 }  // namespace teachos::arch::context_switching::descriptor_table
diff --git a/arch/x86_64/src/context_switching/descriptor_table/type_field.cpp b/arch/x86_64/src/context_switching/descriptor_table/type_field.cpp
deleted file mode 100644
index d967a97..0000000
--- a/arch/x86_64/src/context_switching/descriptor_table/type_field.cpp
+++ /dev/null
@@ -1,12 +0,0 @@
-#include "arch/context_switching/descriptor_table/type_field.hpp"
-
-namespace teachos::arch::context_switching::descriptor_table
-{
-  type_field::type_field(uint8_t flags)
-      : _flags(flags)
-  {
-    // Nothing to do.
-  }
-
-  auto type_field::contains_flags(std::bitset<4U> other) const -> bool { return (_flags & other) == other; }
-}  // namespace teachos::arch::context_switching::descriptor_table