wip context switch in asm

3 files changed, 50 insertions, 11 deletions

diff --git a/arch/x86_64/include/arch/boot/pointers.hpp b/arch/x86_64/include/arch/boot/pointers.hpp
index fe9c657..f0878f9 100644
--- a/arch/x86_64/include/arch/boot/pointers.hpp
+++ b/arch/x86_64/include/arch/boot/pointers.hpp
@@ -9,6 +9,7 @@ namespace teachos::arch::boot
    * @brief Address pointing to the start of the multiboot information structure.
    */
   extern "C" size_t const multiboot_information_pointer;
+  extern "C" auto context_switch() -> void;
 
 }  // namespace teachos::arch::boot
 
diff --git a/arch/x86_64/src/boot/boot.s b/arch/x86_64/src/boot/boot.s
index 7932045..85ae1a1 100644
--- a/arch/x86_64/src/boot/boot.s
+++ b/arch/x86_64/src/boot/boot.s
@@ -352,6 +352,35 @@ prepare_page_maps:
 .section .boot_text, "ax", @progbits
 .code64
 
+.global context_switch
+context_switch:
+    // ring 3 data with bottom 2 bits set for ring 3
+	mov $((4 * 16) | 3), %rax
+    mov %rax, %ds
+    mov %rax, %es
+    mov %rax, %fs
+    mov %rax, %gs
+    // SS is handled by iret https://wiki.osdev.org/Getting_to_Ring_3
+
+	// set up the stack frame iret expects
+	mov %rsp, %rax
+    // user data selector
+	push $((4 * 16) | 3)
+    // current exp
+	push %rax
+    // push eflags
+	pushf
+    // push code selector (ring 3 code with bottom 2 bits set for ring 3)
+	push $((3 * 16) | 3)
+    // instruction address to return to
+	push test_function
+
+	iret
+
+test_function:
+    cli
+    ret
+
 _transition_to_long_mode:
     xor %rax, %rax
     mov %rax, %ss
diff --git a/arch/x86_64/src/kernel/main.cpp b/arch/x86_64/src/kernel/main.cpp
index 7d4173e..52799f0 100644
--- a/arch/x86_64/src/kernel/main.cpp
+++ b/arch/x86_64/src/kernel/main.cpp
@@ -52,12 +52,24 @@ namespace teachos::arch::kernel
   }
 
   [[gnu::naked]]
-  auto push_code_segment(context_switching::interrupt_descriptor_table::segment_selector segment_selector) -> void
+  auto push_code_segment(context_switching::interrupt_descriptor_table::segment_selector segment_selector_a,
+                         context_switching::interrupt_descriptor_table::segment_selector segment_selector_b) -> void
   {
     asm volatile("push %%rbp\n"
                  "push %[input]"
                  : /* No output from call */
-                 : [input] "m"(segment_selector));
+                 : [input] "m"(segment_selector_a));
+    asm volatile("mov %[input], %%ax\n"
+                 "mov %%ax, %%ss\n"
+                 "mov %%ax, %%ds\n"
+                 "mov %%ax, %%es\n"
+                 "mov %%ax, %%fs\n"
+                 "mov %%ax, %%gs"
+                 : /* No output from call */
+                 : [input] "m"(segment_selector_b));
+    asm volatile("iret"
+                 : /* No output from call */
+                 : /* No input to call */);
   }
 
   [[gnu::naked]]
@@ -88,16 +100,13 @@ namespace teachos::arch::kernel
 
     // - Push return instruction pointer
     // - Push return code segment selector
-    context_switching::interrupt_descriptor_table::segment_selector user_code_segment_selector{
-        3U, context_switching::interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_USER};
-    push_code_segment(user_code_segment_selector);
-
-    context_switching::interrupt_descriptor_table::segment_selector user_data_segment_selector{
-        4U, context_switching::interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_USER};
-    kernel::cpu::set_segment_registers(user_data_segment_selector);
+    // context_switching::interrupt_descriptor_table::segment_selector user_code_segment_selector{
+    //     3U, context_switching::interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_USER};
+    // context_switching::interrupt_descriptor_table::segment_selector user_data_segment_selector{
+    //     4U, context_switching::interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_USER};
+    // push_code_segment(user_code_segment_selector, user_data_segment_selector);
 
-    // IRET
-    iret();
+    boot::context_switch();
 
     (void)descriptor_tables;
   }