add wip context switch to user mode

9 files changed, 96 insertions, 61 deletions

diff --git a/arch/x86_64/CMakeLists.txt b/arch/x86_64/CMakeLists.txt
index 5e87594..0d52463 100644
--- a/arch/x86_64/CMakeLists.txt
+++ b/arch/x86_64/CMakeLists.txt
@@ -13,7 +13,7 @@ target_sources("_kernel" PRIVATE
   "src/kernel/cpu/if.cpp"
   "src/kernel/cpu/jmp.cpp"
   "src/kernel/cpu/msr.cpp"
-  "src/kernel/cpu/ss.cpp"
+  "src/kernel/cpu/segment_register.cpp"
   "src/kernel/cpu/tlb.cpp"
   "src/kernel/cpu/tr.cpp"
 )
diff --git a/arch/x86_64/include/arch/boot/pointers.hpp b/arch/x86_64/include/arch/boot/pointers.hpp
index 9bf5cfd..fe9c657 100644
--- a/arch/x86_64/include/arch/boot/pointers.hpp
+++ b/arch/x86_64/include/arch/boot/pointers.hpp
@@ -10,11 +10,6 @@ namespace teachos::arch::boot
    */
   extern "C" size_t const multiboot_information_pointer;
 
-  /**
-   * @brief Address pointing to the method that clears all segment registers.
-   */
-  extern "C" void reload_segment_register();
-
 }  // namespace teachos::arch::boot
 
 #endif  // TEACHOS_ARCH_X86_64_BOOT_POINTERS_HPP
diff --git a/arch/x86_64/include/arch/kernel/cpu/segment_register.hpp b/arch/x86_64/include/arch/kernel/cpu/segment_register.hpp
new file mode 100644
index 0000000..bd244fd
--- /dev/null
+++ b/arch/x86_64/include/arch/kernel/cpu/segment_register.hpp
@@ -0,0 +1,23 @@
+#ifndef TEACHOS_ARCH_X86_64_KERNEL_CPU_SEGMENT_REGISTER_HPP
+#define TEACHOS_ARCH_X86_64_KERNEL_CPU_SEGMENT_REGISTER_HPP
+
+#include "arch/context_switching/interrupt_descriptor_table/segment_selector.hpp"
+
+namespace teachos::arch::kernel::cpu
+{
+  /**
+   * @brief Clear all segment registers.
+   */
+  [[gnu::naked]]
+  auto reload_segment_registers() -> void;
+
+  /**
+   * @brief Set the value of all segment registers.
+   *
+   * @param segment_selector
+   */
+  auto set_segment_registers(context_switching::interrupt_descriptor_table::segment_selector segment_selector) -> void;
+
+}  // namespace teachos::arch::kernel::cpu
+
+#endif  // TEACHOS_ARCH_X86_64_KERNEL_CPU_SEGMENT_REGISTER_HPP
diff --git a/arch/x86_64/include/arch/kernel/cpu/ss.hpp b/arch/x86_64/include/arch/kernel/cpu/ss.hpp
deleted file mode 100644
index b5fa5e3..0000000
--- a/arch/x86_64/include/arch/kernel/cpu/ss.hpp
+++ /dev/null
@@ -1,27 +0,0 @@
-#ifndef TEACHOS_ARCH_X86_64_KERNEL_CPU_SS_HPP
-#define TEACHOS_ARCH_X86_64_KERNEL_CPU_SS_HPP
-
-#include "arch/context_switching/interrupt_descriptor_table/segment_selector.hpp"
-
-#include <bitset>
-#include <cstdint>
-
-namespace teachos::arch::kernel::cpu
-{
-  /**
-   * @brief Reads the current value of the stack segment (SS) register.
-   *
-   * @return The current SS register value.
-   */
-  auto read_ss() -> context_switching::interrupt_descriptor_table::segment_selector;
-
-  /**
-   * @brief Writes a new value to the stack segment (SS) register.
-   *
-   * @param selector The segment selector to be written to SS.
-   */
-  auto write_ss(context_switching::interrupt_descriptor_table::segment_selector selector) -> void;
-
-}  // namespace teachos::arch::kernel::cpu
-
-#endif  // TEACHOS_ARCH_X86_64_KERNEL_CPU_SS_HPP
diff --git a/arch/x86_64/src/boot/boot.s b/arch/x86_64/src/boot/boot.s
index 38a8af4..7932045 100644
--- a/arch/x86_64/src/boot/boot.s
+++ b/arch/x86_64/src/boot/boot.s
@@ -352,11 +352,7 @@ prepare_page_maps:
 .section .boot_text, "ax", @progbits
 .code64
 
-.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.
+_transition_to_long_mode:
     xor %rax, %rax
     mov %rax, %ss
     mov %rax, %ds
@@ -364,11 +360,6 @@ reload_segment_register:
     mov %rax, %fs
     mov %rax, %gs
 
-    ret
-
-_transition_to_long_mode:
-    call reload_segment_register
-
     movl $0xb8000, (vga_buffer_pointer)
 
     call _init
diff --git a/arch/x86_64/src/context_switching/main.cpp b/arch/x86_64/src/context_switching/main.cpp
index 6614065..124df93 100644
--- a/arch/x86_64/src/context_switching/main.cpp
+++ b/arch/x86_64/src/context_switching/main.cpp
@@ -1,9 +1,9 @@
 #include "arch/context_switching/main.hpp"
 
-#include "arch/boot/pointers.hpp"
 #include "arch/exception_handling/assert.hpp"
 #include "arch/kernel/cpu/if.hpp"
 #include "arch/kernel/cpu/jmp.hpp"
+#include "arch/kernel/cpu/segment_register.hpp"
 #include "arch/kernel/cpu/tr.hpp"
 
 namespace teachos::arch::context_switching
@@ -17,7 +17,7 @@ namespace teachos::arch::context_switching
 
     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::far_pointer pointer{&kernel::cpu::reload_segment_registers, segment_selector};
     kernel::cpu::jmp(pointer);
 
     segment_descriptor_table::update_task_state_segment_register();
diff --git a/arch/x86_64/src/kernel/cpu/segment_register.cpp b/arch/x86_64/src/kernel/cpu/segment_register.cpp
new file mode 100644
index 0000000..f70c558
--- /dev/null
+++ b/arch/x86_64/src/kernel/cpu/segment_register.cpp
@@ -0,0 +1,34 @@
+#include "arch/kernel/cpu/segment_register.hpp"
+
+#include "arch/context_switching/interrupt_descriptor_table/segment_selector.hpp"
+
+namespace teachos::arch::kernel::cpu
+{
+  [[gnu::naked]]
+  auto reload_segment_registers() -> void
+  {
+    asm volatile("xor %rax, %rax\n"
+                 "mov %rax, %ss\n"
+                 "mov %rax, %ds\n"
+                 "mov %rax, %es\n"
+                 "mov %rax, %fs\n"
+                 "mov %rax, %gs\n"
+                 "ret");
+  }
+
+  [[gnu::naked]]
+  auto set_segment_registers(context_switching::interrupt_descriptor_table::segment_selector segment_selector) -> void
+  {
+    asm volatile("xor %%rax, %%rax\n"
+                 "mov %[input], %%ax\n"
+                 "mov %%rax, %%ss\n"
+                 "mov %%rax, %%ds\n"
+                 "mov %%rax, %%es\n"
+                 "mov %%rax, %%fs\n"
+                 "mov %%rax, %%gs\n"
+                 "ret"
+                 : /* No output from call */
+                 : [input] "m"(segment_selector));
+  }
+
+}  // namespace teachos::arch::kernel::cpu
diff --git a/arch/x86_64/src/kernel/cpu/ss.cpp b/arch/x86_64/src/kernel/cpu/ss.cpp
deleted file mode 100644
index 0978eca..0000000
--- a/arch/x86_64/src/kernel/cpu/ss.cpp
+++ /dev/null
@@ -1,16 +0,0 @@
-#include "arch/kernel/cpu/ss.hpp"
-
-namespace teachos::arch::kernel::cpu
-{
-  auto read_ss() -> context_switching::interrupt_descriptor_table::segment_selector
-  {
-    context_switching::interrupt_descriptor_table::segment_selector segment_selector{};
-    asm volatile("mov %%ss, %[output]" : [output] "=m"(segment_selector));
-    return segment_selector;
-  }
-
-  auto write_ss(context_switching::interrupt_descriptor_table::segment_selector selector) -> void
-  {
-    asm volatile("mov %[input], %%ss" : /* no output from call */ : [input] "m"(selector));
-  }
-}  // namespace teachos::arch::kernel::cpu
diff --git a/arch/x86_64/src/kernel/main.cpp b/arch/x86_64/src/kernel/main.cpp
index 7782d30..7d4173e 100644
--- a/arch/x86_64/src/kernel/main.cpp
+++ b/arch/x86_64/src/kernel/main.cpp
@@ -1,9 +1,11 @@
 #include "arch/kernel/main.hpp"
 
 #include "arch/boot/pointers.hpp"
+#include "arch/context_switching/interrupt_descriptor_table/segment_selector.hpp"
 #include "arch/context_switching/main.hpp"
 #include "arch/kernel/cpu/if.hpp"
 #include "arch/kernel/cpu/jmp.hpp"
+#include "arch/kernel/cpu/segment_register.hpp"
 #include "arch/memory/heap/bump_allocator.hpp"
 #include "arch/memory/heap/global_heap_allocator.hpp"
 #include "arch/memory/main.hpp"
@@ -49,6 +51,23 @@ namespace teachos::arch::kernel
     delete test9;
   }
 
+  [[gnu::naked]]
+  auto push_code_segment(context_switching::interrupt_descriptor_table::segment_selector segment_selector) -> void
+  {
+    asm volatile("push %%rbp\n"
+                 "push %[input]"
+                 : /* No output from call */
+                 : [input] "m"(segment_selector));
+  }
+
+  [[gnu::naked]]
+  auto iret() -> void
+  {
+    asm volatile("iret"
+                 : /* No output from call */
+                 : /* No input to call */);
+  }
+
   auto main() -> void
   {
     video::vga::text::clear();
@@ -64,6 +83,22 @@ namespace teachos::arch::kernel
     heap_test();
 
     decltype(auto) descriptor_tables = context_switching::initialize_descriptor_tables();
+
+    // - Clear NT flag in EFLAGS register (for far return)
+
+    // - 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);
+
+    // IRET
+    iret();
+
     (void)descriptor_tables;
   }
 }  // namespace teachos::arch::kernel