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

Fix GDT and CS reload

See merge request teachos/kernel!5

4 files changed, 21 insertions, 17 deletions

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)
   {