Remove zomby code and fix 32-bit compability crash

2 files changed, 8 insertions, 31 deletions

diff --git a/arch/x86_64/src/context_switching/main.cpp b/arch/x86_64/src/context_switching/main.cpp
index 7449d84..06c0810 100644
--- a/arch/x86_64/src/context_switching/main.cpp
+++ b/arch/x86_64/src/context_switching/main.cpp
@@ -20,8 +20,6 @@ namespace teachos::arch::context_switching
 
     constexpr interrupt_descriptor_table::segment_selector KERNEL_CODE_SEGMENT_SELECTOR{
         1U, interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_KERNEL};
-    constexpr interrupt_descriptor_table::segment_selector KERNEL_DATA_SEGMENT_SELECTOR{
-        2U, interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_KERNEL};
     constexpr kernel::cpu::far_pointer KERNEL_CODE_POINTER{&kernel::cpu::reload_data_segment_registers,
                                                            KERNEL_CODE_SEGMENT_SELECTOR};
     constexpr context_switching::interrupt_descriptor_table::segment_selector USER_CODE_SEGMENT_SELECTOR{
@@ -29,19 +27,7 @@ namespace teachos::arch::context_switching
     constexpr context_switching::interrupt_descriptor_table::segment_selector USER_DATA_SEGMENT_SELECTOR{
         4U, context_switching::interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_USER};
 
-    auto reload_gdtr() -> void
-    {
-      /*asm volatile("pushq $0x8\n\t"            // Push new CS
-                   "lea 1f(%%rip), %%rax\n\t"  // Get address of label 1 into RAX
-                   "pushq %%rax\n\t"           // Push return address
-                   "lretq\n"                   // Far return (loads CS:RIP)
-                   "1:\n\t"                    // Label to return to
-                   :
-                   :
-                   : "rax", "memory");*/
-
-      kernel::cpu::call(KERNEL_CODE_POINTER);
-    }
+    auto reload_gdtr() -> void { kernel::cpu::call(KERNEL_CODE_POINTER); }
 
     auto user_mode_main() -> void
     {
@@ -64,14 +50,11 @@ namespace teachos::arch::context_switching
                    : "memory");
       asm volatile("syscall");
 
-      // TODO: Reading RAX value does not work because the read itself changes the RAX value?!
-      // asm volatile("mov %%rax, %[output]" : [output] "=r"(syscall_value));
-
-      // TODO: Causes a general protection fault after the sysreturn?
-      // If removed instead it will cause a general protection fault after leaving this main method to return to kernel
-      // mode. But CS and SS are still configured for User mode.
-      /*video::vga::text::write("Successfully made a SYSCALL and returned with SYSRETQ!",
-                              video::vga::text::common_attributes::green_on_black);*/
+      // Reading RAX decrements value by one in 32-bit compatability mode it also crashes vga write, therfore use
+      // SYSRETQ instead of SYSRET so we do not return into 32-bit compatability mode.
+      asm volatile("mov %%rax, %[output]" : [output] "=r"(syscall_number));
+      video::vga::text::write("Successfully made a SYSCALL and returned with SYSRETQ!",
+                              video::vga::text::common_attributes::green_on_black);
     }
 
     auto syscall_handler() -> void
@@ -103,11 +86,7 @@ namespace teachos::arch::context_switching
                    : [input] "r"(result)
                    : "memory");
 
-      // Use SYSRET instead of SYSRETQ, because the latter would add 0x10 to bits [48:63] of IA32_STAR_ADDRESS for the
-      // Code Segment. But only add 0x8 to bits [48:63] of IA32_STAR_ADDRESS for the Stack Segment, which means either
-      // the Stack Segment or Code Segment is wrong. Whereas the former does not add 0x10 for the Code Segment and
-      // therefore fixes the aformentioned issue.
-      asm volatile("sysret");
+      asm volatile("sysretq");
     }
 
     auto enable_systemcall() -> void
@@ -117,8 +96,7 @@ namespace teachos::arch::context_switching
       kernel::cpu::write_msr(IA32_FMASK_ADDRESS, 0U);
 
       uint64_t const kernel_cs = KERNEL_CODE_SEGMENT_SELECTOR;
-      uint64_t const user_cs = USER_CODE_SEGMENT_SELECTOR;
-      uint64_t const star_value = (kernel_cs << 32) | (user_cs << 48);
+      uint64_t const star_value = (kernel_cs << 32) | (kernel_cs << 48);
       kernel::cpu::write_msr(IA32_STAR_ADDRESS, star_value);
 
       kernel::cpu::set_efer_bit(kernel::cpu::efer_flags::SCE);
diff --git a/arch/x86_64/src/kernel/cpu/call.cpp b/arch/x86_64/src/kernel/cpu/call.cpp
index 6564b76..98fa248 100644
--- a/arch/x86_64/src/kernel/cpu/call.cpp
+++ b/arch/x86_64/src/kernel/cpu/call.cpp
@@ -5,6 +5,5 @@ namespace teachos::arch::kernel::cpu
   auto call(far_pointer pointer) -> void
   {
     asm volatile("rex64 lcall *%[input]" : /* no output from call */ : [input] "m"(pointer));
-    // asm volatile("ljmp *%0" : : "m"(pointer));
   }
 }  // namespace teachos::arch::kernel::cpu