write wrapper function for syscall

10 files changed, 186 insertions, 108 deletions

diff --git a/arch/x86_64/CMakeLists.txt b/arch/x86_64/CMakeLists.txt
index 21dbddd..0b4eafe 100644
--- a/arch/x86_64/CMakeLists.txt
+++ b/arch/x86_64/CMakeLists.txt
@@ -100,6 +100,8 @@ target_sources("_context" PRIVATE
   "src/context_switching/segment_descriptor_table/segment_descriptor_base.cpp"
   "src/context_switching/segment_descriptor_table/segment_descriptor_extension.cpp"
   "src/context_switching/main.cpp"
+  "src/context_switching/syscall/main.cpp"
+  "src/context_switching/syscall/syscall_handler.cpp"
   "src/context_switching/interrupt_descriptor_table/gate_descriptor.cpp"
   "src/context_switching/interrupt_descriptor_table/idt_flags.cpp"
   "src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table_pointer.cpp"
diff --git a/arch/x86_64/include/arch/context_switching/syscall/main.hpp b/arch/x86_64/include/arch/context_switching/syscall/main.hpp
new file mode 100644
index 0000000..c75268a
--- /dev/null
+++ b/arch/x86_64/include/arch/context_switching/syscall/main.hpp
@@ -0,0 +1,28 @@
+#ifndef TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SYSCALL_MAIN_HPP
+#define TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SYSCALL_MAIN_HPP
+
+#include "arch/context_switching/syscall/syscall_handler.hpp"
+
+#include <array>
+#include <cstdint>
+#include <optional>
+
+namespace teachos::arch::context_switching::syscall
+{
+  struct arguments
+  {
+    uint64_t arg_0{};
+    uint64_t arg_1{};
+    uint64_t arg_2{};
+    uint64_t arg_3{};
+    uint64_t arg_4{};
+    uint64_t arg_5{};
+  };
+
+  auto enable_syscall() -> void;
+
+  auto syscall(type syscall_number, arguments args = {}) -> uint64_t;
+
+}  // namespace teachos::arch::context_switching::syscall
+
+#endif  // TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SYSCALL_MAIN_HPP
diff --git a/arch/x86_64/include/arch/context_switching/syscall/syscall_handler.hpp b/arch/x86_64/include/arch/context_switching/syscall/syscall_handler.hpp
new file mode 100644
index 0000000..e076995
--- /dev/null
+++ b/arch/x86_64/include/arch/context_switching/syscall/syscall_handler.hpp
@@ -0,0 +1,23 @@
+#ifndef TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SYSCALL_SYSCALL_HANDLER_HPP
+#define TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SYSCALL_SYSCALL_HANDLER_HPP
+
+#include <cstdint>
+
+namespace teachos::arch::context_switching::syscall
+{
+  enum type : uint64_t
+  {
+    WRITE = 1U
+  };
+
+  /**
+   * @brief Handler for SYSCALL instruction. Calls a specific implementation based
+   * on the register RAX.
+   *
+   * @return Returns with SYSRETQ
+   */
+  auto syscall_handler() -> void;
+
+}  // namespace teachos::arch::context_switching::syscall
+
+#endif  // TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_SYSCALL_SYSCALL_HANDLER_HPP
diff --git a/arch/x86_64/include/arch/interrupt_handling/generic_interrupt_handler.hpp b/arch/x86_64/include/arch/interrupt_handling/generic_interrupt_handler.hpp
index 866d15d..8091a58 100644
--- a/arch/x86_64/include/arch/interrupt_handling/generic_interrupt_handler.hpp
+++ b/arch/x86_64/include/arch/interrupt_handling/generic_interrupt_handler.hpp
@@ -29,14 +29,6 @@ namespace teachos::arch::interrupt_handling
   [[gnu::interrupt]] [[gnu::section(".interrupt_text")]]
   auto generic_interrupt_handler(interrupt_frame * frame) -> void;
 
-  /**
-   * @brief Interrupt handler function for syscalls (INT 0x80).
-   *
-   * @param frame Pointer to the interrupt frame containing CPU state.
-   */
-  [[gnu::interrupt]] [[gnu::section(".interrupt_text")]]
-  auto syscall_interrupt_handler(interrupt_frame * frame) -> void;
-
 }  // namespace teachos::arch::interrupt_handling
 
 #endif  // TEACHOS_ARCH_X86_64_INTERRUPT_HANDLING_GENERIC_INTERRUPT_HANDLER_HPP
diff --git a/arch/x86_64/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp b/arch/x86_64/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp
index c041198..7aa0859 100644
--- a/arch/x86_64/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp
+++ b/arch/x86_64/src/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.cpp
@@ -26,11 +26,6 @@ namespace teachos::arch::context_switching::interrupt_descriptor_table
         interrupt_descriptor_table.at(i) = {selector, ist, flags, offset};
       }
 
-      interrupt_descriptor_table.at(0x80) = {
-          segment_selector{1U, segment_selector::REQUEST_LEVEL_KERNEL}, ist_offset{0U},
-          idt_flags{idt_flags::DESCRIPTOR_LEVEL_USER | idt_flags::TRAP_GATE | idt_flags::PRESENT},
-          uint64_t{reinterpret_cast<uint64_t>(interrupt_handling::syscall_interrupt_handler)}};
-
       return interrupt_descriptor_table;
     }
   }  // namespace
diff --git a/arch/x86_64/src/context_switching/main.cpp b/arch/x86_64/src/context_switching/main.cpp
index 06c0810..7fe159e 100644
--- a/arch/x86_64/src/context_switching/main.cpp
+++ b/arch/x86_64/src/context_switching/main.cpp
@@ -1,11 +1,11 @@
 #include "arch/context_switching/main.hpp"
 
 #include "arch/boot/pointers.hpp"
+#include "arch/context_switching/syscall/main.hpp"
 #include "arch/exception_handling/assert.hpp"
 #include "arch/kernel/cpu/call.hpp"
 #include "arch/kernel/cpu/control_register.hpp"
 #include "arch/kernel/cpu/if.hpp"
-#include "arch/kernel/cpu/msr.hpp"
 #include "arch/kernel/cpu/segment_register.hpp"
 #include "arch/kernel/cpu/tr.hpp"
 #include "arch/video/vga/text.hpp"
@@ -14,10 +14,6 @@ namespace teachos::arch::context_switching
 {
   namespace
   {
-    auto constexpr IA32_STAR_ADDRESS = 0xC0000081;
-    auto constexpr IA32_LSTAR_ADDRESS = 0xC0000082;
-    auto constexpr IA32_FMASK_ADDRESS = 0xC0000084;
-
     constexpr interrupt_descriptor_table::segment_selector KERNEL_CODE_SEGMENT_SELECTOR{
         1U, interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_KERNEL};
     constexpr kernel::cpu::far_pointer KERNEL_CODE_POINTER{&kernel::cpu::reload_data_segment_registers,
@@ -31,8 +27,6 @@ namespace teachos::arch::context_switching
 
     auto user_mode_main() -> void
     {
-      video::vga::text::write("Successfully entered user mode!", video::vga::text::common_attributes::green_on_black);
-
       // RFLAGS is saved into R11, RIP of the next instruction into RCX
       // Required for SYSRETURN to know where to return too.
       // Additional state needs to be saved by calling convention:
@@ -43,65 +37,16 @@ namespace teachos::arch::context_switching
 
       // Actual Source: https://man7.org/linux/man-pages/man2/syscall.2.html More cleare documentation:
       // https://sys.readthedocs.io/en/latest/doc/05_calling_system_calls.html
-      uint64_t syscall_number = 60U;
-      asm volatile("mov %[input], %%rax"
-                   : /* no output from call */
-                   : [input] "r"(syscall_number)
-                   : "memory");
-      asm volatile("syscall");
-
-      // 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
-    {
-      uint64_t syscall_number, arg_0, arg_1, arg_2, arg_3, arg_4, arg_5 = {};
-      asm volatile("mov %%rax, %[output]" : [output] "=r"(syscall_number));
-      asm volatile("mov %%rdi, %[output]" : [output] "=r"(arg_0));
-      asm volatile("mov %%rsi, %[output]" : [output] "=r"(arg_1));
-      asm volatile("mov %%rdx, %[output]" : [output] "=r"(arg_2));
-      asm volatile("mov %%r10, %[output]" : [output] "=r"(arg_3));
-      asm volatile("mov %%r8, %[output]" : [output] "=r"(arg_4));
-      asm volatile("mov %%r9, %[output]" : [output] "=r"(arg_5));
-
-      switch (syscall_number)
+      const char syscall_message[32] = "Successfully entered user mode!";
+      auto error = syscall::syscall(syscall::WRITE, {reinterpret_cast<uint64_t>(&syscall_message)});
+
+      if (!error)
       {
-        case 1:
-          // Write VGA
-          break;
-        case 60U:
-          // Exit
-          break;
-        default:
-          break;
+        video::vga::text::write("Successfully made a SYSCALL and returned with SYSRETQ!",
+                                video::vga::text::common_attributes::green_on_black);
       }
-
-      uint64_t result = 0U;
-      asm volatile("mov %[input], %%rax"
-                   : /* no output from call */
-                   : [input] "r"(result)
-                   : "memory");
-
-      asm volatile("sysretq");
     }
-
-    auto enable_systemcall() -> void
-    {
-      uint64_t const syscall_function = reinterpret_cast<uint64_t>(syscall_handler);
-      kernel::cpu::write_msr(IA32_LSTAR_ADDRESS, syscall_function);
-      kernel::cpu::write_msr(IA32_FMASK_ADDRESS, 0U);
-
-      uint64_t const kernel_cs = KERNEL_CODE_SEGMENT_SELECTOR;
-      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);
-    }
-
   }  // namespace
 
   auto initialize_descriptor_tables() -> descriptor_tables
@@ -129,7 +74,7 @@ namespace teachos::arch::context_switching
 
   auto switch_to_user_mode() -> void
   {
-    enable_systemcall();
+    syscall::enable_syscall();
     switch_context(USER_DATA_SEGMENT_SELECTOR, USER_CODE_SEGMENT_SELECTOR, user_mode_main);
   }
 
diff --git a/arch/x86_64/src/context_switching/syscall/main.cpp b/arch/x86_64/src/context_switching/syscall/main.cpp
new file mode 100644
index 0000000..e90f503
--- /dev/null
+++ b/arch/x86_64/src/context_switching/syscall/main.cpp
@@ -0,0 +1,57 @@
+#include "arch/context_switching/syscall/main.hpp"
+
+#include "arch/context_switching/interrupt_descriptor_table/segment_selector.hpp"
+#include "arch/exception_handling/assert.hpp"
+#include "arch/exception_handling/panic.hpp"
+#include "arch/kernel/cpu/msr.hpp"
+
+#include <cstdint>
+
+namespace teachos::arch::context_switching::syscall
+{
+  namespace
+  {
+    constexpr interrupt_descriptor_table::segment_selector KERNEL_CODE_SEGMENT_SELECTOR{
+        1U, interrupt_descriptor_table::segment_selector::REQUEST_LEVEL_KERNEL};
+
+    auto constexpr IA32_STAR_ADDRESS = 0xC0000081;
+    auto constexpr IA32_LSTAR_ADDRESS = 0xC0000082;
+    auto constexpr IA32_FMASK_ADDRESS = 0xC0000084;
+
+  }  // namespace
+
+  auto enable_syscall() -> void
+  {
+    uint64_t const syscall_function = reinterpret_cast<uint64_t>(syscall_handler);
+    kernel::cpu::write_msr(IA32_LSTAR_ADDRESS, syscall_function);
+    kernel::cpu::write_msr(IA32_FMASK_ADDRESS, 0U);
+
+    uint64_t const kernel_cs = KERNEL_CODE_SEGMENT_SELECTOR;
+    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);
+  }
+
+  auto syscall(type syscall_number, arguments args) -> uint64_t
+  {
+    asm volatile("mov %[input], %%rax"
+                 : /* no output from call */
+                 : [input] "m"(syscall_number)
+                 : "memory");
+
+    asm volatile("mov %[input], %%rdi " : /* no output from call */ : [input] "m"(args.arg_0) : "memory");
+    asm volatile("mov %[input], %%rsi" : /* no output from call */ : [input] "m"(args.arg_1) : "memory");
+    asm volatile("mov %[input], %%rdx" : /* no output from call */ : [input] "m"(args.arg_2) : "memory");
+    asm volatile("mov %[input], %%r10" : /* no output from call */ : [input] "m"(args.arg_3) : "memory");
+    asm volatile("mov %[input], %%r8" : /* no output from call */ : [input] "m"(args.arg_4) : "memory");
+    asm volatile("mov %[input], %%r9" : /* no output from call */ : [input] "m"(args.arg_5) : "memory");
+
+    asm volatile("syscall");
+
+    uint64_t result{};
+    asm volatile("mov %%rax, %[output]" : [output] "=m"(result));
+    return result;
+  }
+
+}  // namespace teachos::arch::context_switching::syscall
\ No newline at end of file
diff --git a/arch/x86_64/src/context_switching/syscall/syscall_handler.cpp b/arch/x86_64/src/context_switching/syscall/syscall_handler.cpp
new file mode 100644
index 0000000..f6e1c9e
--- /dev/null
+++ b/arch/x86_64/src/context_switching/syscall/syscall_handler.cpp
@@ -0,0 +1,68 @@
+#include "arch/context_switching/syscall/syscall_handler.hpp"
+
+#include "arch/exception_handling/panic.hpp"
+#include "arch/video/vga/text.hpp"
+
+namespace teachos::arch::context_switching::syscall
+{
+
+  namespace
+  {
+    auto write_to_vga_buffer(uint64_t buffer)
+    {
+      video::vga::text::write(reinterpret_cast<const char *>(buffer),
+                              video::vga::text::common_attributes::green_on_black);
+    }
+  }  // namespace
+
+  auto syscall_handler() -> void
+  {
+    // Saving state of rcx and r11 because it is required by sysretq to function.
+    // Calls to other functions potentially overwrite these registers, because of
+    // callee saved calling convention.
+    uint64_t return_instruction_pointer, rflags = {};
+    asm volatile("mov %%rcx, %[output]" : [output] "=m"(return_instruction_pointer));
+    asm volatile("mov %%r11, %[output]" : [output] "=m"(rflags));
+
+    uint64_t syscall_number, arg_0, arg_1, arg_2, arg_3, arg_4, arg_5 = {};
+    asm volatile("mov %%rdi, %[output]" : [output] "=m"(arg_0));
+    asm volatile("mov %%rsi, %[output]" : [output] "=m"(arg_1));
+    asm volatile("mov %%rdx, %[output]" : [output] "=m"(arg_2));
+    asm volatile("mov %%r10, %[output]" : [output] "=m"(arg_3));
+    asm volatile("mov %%r8, %[output]" : [output] "=m"(arg_4));
+    asm volatile("mov %%r9, %[output]" : [output] "=m"(arg_5));
+
+    // RAX is read last, because paired with our type enum, we can use it to check
+    // if the register has been written by the compiled code between executing the syscall
+    // and now.
+    asm volatile("mov %%rax, %[output]" : [output] "=m"(syscall_number));
+
+    switch (static_cast<type>(syscall_number))
+    {
+      case WRITE:
+        write_to_vga_buffer(arg_0);
+        break;
+      default:
+        teachos::arch::exception_handling::panic("[Syscall Handler] Invalid syscall number");
+        break;
+    }
+
+    uint64_t result = 0U;
+    asm volatile("mov %[input], %%rax"
+                 : /* no output from call */
+                 : [input] "m"(result)
+                 : "memory");
+
+    asm volatile("mov %[input], %%rcx"
+                 : /* no output from call */
+                 : [input] "m"(return_instruction_pointer)
+                 : "memory");
+    asm volatile("mov %[input], %%r11"
+                 : /* no output from call */
+                 : [input] "m"(rflags)
+                 : "memory");
+
+    asm volatile("sysretq");
+  }
+
+}  // namespace teachos::arch::context_switching::syscall
\ No newline at end of file
diff --git a/arch/x86_64/src/interrupt_handling/generic_interrupt_handler.cpp b/arch/x86_64/src/interrupt_handling/generic_interrupt_handler.cpp
index 60fb50c..8e2c62d 100644
--- a/arch/x86_64/src/interrupt_handling/generic_interrupt_handler.cpp
+++ b/arch/x86_64/src/interrupt_handling/generic_interrupt_handler.cpp
@@ -9,30 +9,4 @@ namespace teachos::arch::interrupt_handling
     (void)frame;
     video::vga::text::write("An Interrupt occurred.", video::vga::text::common_attributes::green_on_black);
   }
-
-  auto syscall_interrupt_handler(interrupt_frame * frame) -> void
-  {
-    // RDI, RSI, RDX, RCX, R8, R9
-    // RDI -> SYSCALL number
-    // Others are arguments
-
-    // TODO: The registers are not available here. We need to set them up on the stack
-    // and access them via argument.
-
-    uint64_t syscall_number{};
-    asm volatile("mov %%rdi, %0" : "=r"(syscall_number));
-
-    // Handle system call based on the number
-    switch (syscall_number)
-    {
-      case 1:
-        video::vga::text::write("SYSCALL 1.", video::vga::text::common_attributes::green_on_black);
-        break;
-      default:
-        // Handle unknown syscall
-        break;
-    }
-
-    (void)frame;
-  }
 }  // namespace teachos::arch::interrupt_handling
diff --git a/arch/x86_64/src/kernel/cpu/control_register.cpp b/arch/x86_64/src/kernel/cpu/control_register.cpp
index a39a360..41b8cd7 100644
--- a/arch/x86_64/src/kernel/cpu/control_register.cpp
+++ b/arch/x86_64/src/kernel/cpu/control_register.cpp
@@ -23,9 +23,6 @@ namespace teachos::arch::kernel::cpu
       case control_register::CR4:
         asm volatile("mov %%cr4, %[output]" : [output] "=r"(current_value));
         break;
-      default:
-        exception_handling::panic("[Control Register] Attempted to read non-existent or reserved control register");
-        break;
     }
     return current_value;
   }
@@ -58,9 +55,6 @@ namespace teachos::arch::kernel::cpu
                      : [input] "r"(new_value)
                      : "memory");
         break;
-      default:
-        exception_handling::panic("[Control Register] Attempted to write non-existent or reserved control register");
-        break;
     }
   }