Merge branch 'fmorgner/patch-context-switching' into 'feat_inital_context_switching'

Fix GDT and CS reload

See merge request teachos/kernel!5

9 files changed, 42 insertions, 29 deletions

diff --git a/.vscode/tasks.json b/.vscode/tasks.json
index 2e076e4..6fc5711 100644
--- a/.vscode/tasks.json
+++ b/.vscode/tasks.json
@@ -10,6 +10,9 @@
                 "-s",
                 "-m",
                 "32M",
+                "-no-reboot",
+                "-d",
+                "int,cpu_reset",
                 "-cdrom",
                 "${workspaceFolder}/build/teachos-${input:build_type}.iso"
             ],
diff --git a/arch/x86_64/include/arch/boot/pointers.hpp b/arch/x86_64/include/arch/boot/pointers.hpp
index c08de52..9bf5cfd 100644
--- a/arch/x86_64/include/arch/boot/pointers.hpp
+++ b/arch/x86_64/include/arch/boot/pointers.hpp
@@ -13,7 +13,7 @@ namespace teachos::arch::boot
   /**
    * @brief Address pointing to the method that clears all segment registers.
    */
-  extern "C" size_t reload_segment_register;
+  extern "C" void reload_segment_register();
 
 }  // namespace teachos::arch::boot
 
diff --git a/arch/x86_64/include/arch/context_switching/segment_descriptor_table/gdt_flags.hpp b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/gdt_flags.hpp
index fdf0044..764aec5 100644
--- a/arch/x86_64/include/arch/context_switching/segment_descriptor_table/gdt_flags.hpp
+++ b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/gdt_flags.hpp
@@ -18,17 +18,24 @@ namespace teachos::arch::context_switching::segment_descriptor_table
      */
     enum bitset : uint8_t
     {
-      LENGTH = 1U << 0U,  ///< Defines in IA-32e mode (64-bit code and 32-bit compatability mode) if the segment
-                          ///< contains 64-bit code. Otherwise this bit should always be 0. Enable if instructions are
-                          ///< executed in 64-bit code, otherwise they are executed in compatability 32-bit mode. If bis
-                          ///< is set the DEFAULT_LENGTH bis needs to be 0
+      LONG_MODE = 1U << 1U,  ///< Defines in IA-32e mode (64-bit code and 32-bit compatability mode) if the segment
+                             ///< contains 64-bit code. Otherwise this bit should always be 0. Enable if instructions are
+                             ///< executed in 64-bit code, otherwise they are executed in compatability 32-bit mode. If bis
+                             ///< is set the DEFAULT_LENGTH bis needs to be 0
+
+      // FIXME: Where does this come from, and is this value correct?
       UPPER_BOUND = 1U << 1U,  ///< Specifies the upper bound of the segment for expand down data segment. Enable for 5
                                ///< GiB, 4 KiB otherwise.
+
+      // FIXME: Where does this come from, and is this value correct?
       STACK_POINTER_SIZE = 1U << 1U,  ///< Specifies the size of the Stack Pointer (SP) for stack segments used for
                                       ///< implicit stack operations. Enable for 32 bit, 16 bit otherwise.
+
+      // FIXME: Where does this come from, and is this value correct?
       DEFAULT_LENGTH = 1U << 1U,      ///< Indicates the default length for code segments with effective addresses and
                                       ///< operands. Enable for 32 bit, 16 bit otherwise.
-      GRANULARITY = 1U << 2U,  ///< Indicates the size the Limit value in the segment descriptor is scaled by 1 Byte
+
+      GRANULARITY = 1U << 3U,  ///< Indicates the size the Limit value in the segment descriptor is scaled by 1 Byte
                                ///< blocks if the bit is not set or by 4 KiB blocks if the bit is set.
     };
 
diff --git a/arch/x86_64/include/arch/context_switching/segment_descriptor_table/global_descriptor_table_pointer.hpp b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/global_descriptor_table_pointer.hpp
index 13d6f53..6fac2a0 100644
--- a/arch/x86_64/include/arch/context_switching/segment_descriptor_table/global_descriptor_table_pointer.hpp
+++ b/arch/x86_64/include/arch/context_switching/segment_descriptor_table/global_descriptor_table_pointer.hpp
@@ -26,7 +26,7 @@ namespace teachos::arch::context_switching::segment_descriptor_table
     /**
      * @brief Constructor.
      */
-    global_descriptor_table_pointer(uint16_t table_length, global_descriptor_table * address);
+    global_descriptor_table_pointer(uint16_t table_length, segment_descriptor * address);
 
     /**
      * @brief Defaulted three-way comparsion operator.
@@ -35,7 +35,7 @@ namespace teachos::arch::context_switching::segment_descriptor_table
 
   private:
     uint16_t table_length = {};  ///< The amount of segment descriptor entries in the global descriptor table - 1.
-    global_descriptor_table * address = {};  ///< Non-owning pointer to the GDT base address.
+    segment_descriptor * address = {};  ///< Non-owning pointer to the GDT base address.
   };
 }  // namespace teachos::arch::context_switching::segment_descriptor_table
 
diff --git a/arch/x86_64/include/arch/kernel/cpu/jmp.hpp b/arch/x86_64/include/arch/kernel/cpu/jmp.hpp
index 163fac6..0ed38e9 100644
--- a/arch/x86_64/include/arch/kernel/cpu/jmp.hpp
+++ b/arch/x86_64/include/arch/kernel/cpu/jmp.hpp
@@ -10,11 +10,10 @@ namespace teachos::arch::kernel::cpu
   /**
    * @brief Far jump - A jump to an instruction located in a different segment.
    */
-  struct [[gnu::packed]] far_pointer
+  struct far_pointer
   {
-    std::size_t function;  ///< Address of the function we want to jump too. (0- 63)
-    context_switching::interrupt_descriptor_table::segment_selector
-        selector;  ///< Segment selector that shows the segment we want to jump into. (64 - 79)
+    void (*function)();  ///< Address of the function we want to jump too. (0-63)
+    std::uint16_t index; ///< Index of the GDT entry we want to load into register CS. (64-79)
   };
 
   /**
diff --git a/arch/x86_64/src/boot/boot.s b/arch/x86_64/src/boot/boot.s
index bf150a3..108dbe5 100644
--- a/arch/x86_64/src/boot/boot.s
+++ b/arch/x86_64/src/boot/boot.s
@@ -356,6 +356,9 @@ prepare_page_maps:
 
 .global reload_segment_register
 reload_segment_register:
+    // FIXME: maybe we should set the actually correct values here. We'd need to communicate them down from C++.
+    // Alternatively, we could probably implement this as a [[gnu::naked]] function in C++, to have easier access to
+    // arguments and symbols. Maybe later.
     xor %rax, %rax
     mov %rax, %ss
     mov %rax, %ds
diff --git a/arch/x86_64/src/context_switching/main.cpp b/arch/x86_64/src/context_switching/main.cpp
index 5d19f23..a5bd3fb 100644
--- a/arch/x86_64/src/context_switching/main.cpp
+++ b/arch/x86_64/src/context_switching/main.cpp
@@ -13,22 +13,21 @@ namespace teachos::arch::context_switching
     decltype(auto) global_descriptor_table = segment_descriptor_table::initialize_global_descriptor_table();
     decltype(auto) interrupt_descriptor_table = interrupt_descriptor_table::initialize_interrupt_descriptor_table();
 
-    interrupt_descriptor_table::segment_selector segment_selector{
-        1U, interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_KERNEL};
-    kernel::cpu::far_pointer pointer{boot::reload_segment_register, segment_selector};
-    kernel::cpu::jmp(pointer);
+    kernel::cpu::far_pointer pointer{&boot::reload_segment_register, 1 * sizeof(segment_descriptor_table::segment_descriptor)};
+    asm volatile("rex64 lcall *%[far_function_pointer]" : : [far_function_pointer] "m" (pointer));
 
-    // Load task state segment descriptor from the last element in the global descriptor table, done by calculating
-    // offset in bytes to the start of the segment descriptor (5 * 16) = 80
-    uint16_t const tss_selector =
-        (global_descriptor_table.size() - 1) * sizeof(segment_descriptor_table::segment_descriptor);
-    kernel::cpu::load_task_register(tss_selector);
+    // // Load task state segment descriptor from the last element in the global descriptor table, done by calculating
+    // // offset in bytes to the start of the segment descriptor (5 * 16) = 80
+    // uint16_t const tss_selector =
+    //     (global_descriptor_table.size() - 1) * sizeof(segment_descriptor_table::segment_descriptor);
+    // kernel::cpu::load_task_register(tss_selector);
 
-    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.");
+    // 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.");
 
-    kernel::cpu::set_interrupt_flag();
+    // FIXME: We currently cannot enable interrupts, since for some reason, we will later run into what looks like a GP. Maybe because no IDT is loaded? Maybe our boot code segment is not set up correctly?
+    // kernel::cpu::set_interrupt_flag();
 
     descriptor_tables tables = {global_descriptor_table, interrupt_descriptor_table};
     return tables;
diff --git a/arch/x86_64/src/context_switching/segment_descriptor_table/global_descriptor_table.cpp b/arch/x86_64/src/context_switching/segment_descriptor_table/global_descriptor_table.cpp
index e6a489c..37ee778 100644
--- a/arch/x86_64/src/context_switching/segment_descriptor_table/global_descriptor_table.cpp
+++ b/arch/x86_64/src/context_switching/segment_descriptor_table/global_descriptor_table.cpp
@@ -20,12 +20,14 @@ namespace teachos::arch::context_switching::segment_descriptor_table
       uint8_t gdt_flags_bits = gdt_flags::GRANULARITY;
       if (segment_descriptor_type == segment_descriptor_type::CODE_SEGMENT)
       {
-        gdt_flags_bits |= gdt_flags::LENGTH;
+        gdt_flags_bits |= gdt_flags::LONG_MODE;
         access_level_bits |= access_byte::CODE_SEGMENT | access_byte::READABLE;
       }
       else if (segment_descriptor_type == segment_descriptor_type::DATA_SEGMENT)
       {
-        gdt_flags_bits |= gdt_flags::UPPER_BOUND;
+        gdt_flags_bits |= 1 << 2;
+        // FIXME: Look at those bit flags, something seems off.
+        // gdt_flags_bits |= gdt_flags::UPPER_BOUND;
         access_level_bits |= access_byte::WRITABLE;
       }
 
@@ -78,7 +80,7 @@ namespace teachos::arch::context_switching::segment_descriptor_table
     // Calculate the size of the gdt in bytes - 1. This subtraction occurs because the maximum value of Size is 65535,
     // while the GDT can be up to 65536 bytes in length (8192 entries). Further, no GDT can have a size of 0 bytes.
     global_descriptor_table_pointer gdt_pointer{static_cast<uint16_t>((gdt.size() * sizeof(segment_descriptor)) - 1),
-                                                &gdt};
+                                                gdt.data()};
     kernel::cpu::load_global_descriptor_table(gdt_pointer);
 
     auto const stored_gdt_pointer = kernel::cpu::store_global_descriptor_table();
diff --git a/arch/x86_64/src/context_switching/segment_descriptor_table/global_descriptor_table_pointer.cpp b/arch/x86_64/src/context_switching/segment_descriptor_table/global_descriptor_table_pointer.cpp
index 132565f..a4a5de8 100644
--- a/arch/x86_64/src/context_switching/segment_descriptor_table/global_descriptor_table_pointer.cpp
+++ b/arch/x86_64/src/context_switching/segment_descriptor_table/global_descriptor_table_pointer.cpp
@@ -3,7 +3,7 @@
 namespace teachos::arch::context_switching::segment_descriptor_table
 {
   global_descriptor_table_pointer::global_descriptor_table_pointer(uint16_t table_length,
-                                                                   global_descriptor_table * address)
+                                                                   segment_descriptor * address)
       : table_length(table_length)
       , address(address)
   {