wip implement syscall in cpp

4 files changed, 55 insertions, 34 deletions

diff --git a/arch/x86_64/src/boot/boot.s b/arch/x86_64/src/boot/boot.s
index 24b38ca..7932045 100644
--- a/arch/x86_64/src/boot/boot.s
+++ b/arch/x86_64/src/boot/boot.s
@@ -352,31 +352,6 @@ prepare_page_maps:
 .section .boot_text, "ax", @progbits
 .code64
 
-syscall_target:
-    iretq
-
-.global syscall_trampoline 
-syscall_trampoline:
-    /* Write target function pointer in IA32_LSTAR MSR */
-    mov $0xC0000082, %ecx  /* IA32_LSTAR MSR */
-    lea [syscall_target], %rax
-    lea [syscall_target], %rdx
-    shr $32, %rdx
-    wrmsr
-
-    /* Write ... in IA32_LSTAR MSR */
-    mov $0xC0000084, %ecx /* IA32_FMASK MSR */
-    mov $0x0, %rax /* ... lower 32 bits */
-    mov $0x0, %rdx /* ... upper 32 bits */
-    wrmsr
-
-    /* Write Segment selector in IA32_STAR MSR */
-    mov $0xC0000081, %ecx  /* IA32_STAR MSR */
-    mov $0x10, %rax /* SS lower 32 bits */
-    mov $0x0, %rdx /* SS upper 32 bits */
-    wrmsr
-
-
 _transition_to_long_mode:
     xor %rax, %rax
     mov %rax, %ss
diff --git a/arch/x86_64/src/context_switching/main.cpp b/arch/x86_64/src/context_switching/main.cpp
index c949488..85cefe5 100644
--- a/arch/x86_64/src/context_switching/main.cpp
+++ b/arch/x86_64/src/context_switching/main.cpp
@@ -1,6 +1,7 @@
 #include "arch/context_switching/main.hpp"
 
 #include "arch/boot/pointers.hpp"
+#include "arch/context_switching/syscall_handler.hpp"
 #include "arch/exception_handling/assert.hpp"
 #include "arch/kernel/cpu/call.hpp"
 #include "arch/kernel/cpu/control_register.hpp"
@@ -53,15 +54,7 @@ namespace teachos::arch::context_switching
   {
     kernel::cpu::validate_segment_registers(USER_DATA_SEGMENT_SELECTOR, USER_CODE_SEGMENT_SELECTOR);
 
-    // TODO/INFO:
-    // https://stackoverflow.com/questions/46022184/osdev-syscall-sysret-and-sysenter-sysexit-instructions-enabling
-    // https://stackoverflow.com/questions/12806584/what-is-better-int-0x80-or-syscall-in-32-bit-code-on-linux
-    //
-    // People claim that SYSENTER is for 32-Bit, while SYSCALL is for 64-Bit!
-
-    // asm volatile("INT $0x80");
-    // asm volatile("SYSCALL");
-    boot::syscall_trampoline();
+    asm volatile("SYSCALL");
 
     video::vga::text::write("Successfully entered user mode!", video::vga::text::common_attributes::green_on_black);
   }
@@ -79,4 +72,36 @@ namespace teachos::arch::context_switching
     kernel::cpu::set_code_segment_register(data_segment, code_segment, reinterpret_cast<uint64_t>(return_function));
   }
 
+  auto setup_syscall() -> void
+  {
+    uint64_t handler = reinterpret_cast<uint64_t>(syscall_handler);
+    asm volatile(
+        /* Write syscall_handler pointer in IA32_LSTAR MSR */
+        "mov $0xC0000082, %%ecx\n" /* IA32_LSTAR MSR */
+        "mov %[syscall_handler], %%rax"
+        "mov %[syscall_handler], %%rdx"
+        "shr $32, %%rdx\n"
+        "wrmsr\n"
+
+        /* Write RFLAGS Mask in IA32_LSTAR MSR */
+        "mov $0xC0000084, %%ecx\n" /* IA32_FMASK MSR */
+        "mov $0x0, %%rax\n"        /* RFLAGS Mask lower 32 bits */
+        "mov $0x0, %%rdx\n"        /* RFLAGS Mask upper 32 bits */
+        "wrmsr\n"
+
+        /* Write kernel code segment offset in IA32_STAR MSR */
+        "mov $0xC0000081, %%ecx\n" /* IA32_STAR MSR */
+        "mov $0x10, %%rax\n"       /* kernel code segment offset lower 32 bits */
+        "mov $0x0, %%rdx\n"        /* kernel code segment offset upper 32 bits */
+        "wrmsr\n"
+
+        /* Set SCE bit in MSR_EFER (enabling syscall instruction)*/
+        "mov $0xC0000080, %%ecx\n"
+        "rdmsr\n"
+        "or $0x1, %%eax\n"
+        "wrmsr"
+        : /* no output from call */
+        : [syscall_handler] "r"(handler));
+  }
+
 }  // namespace teachos::arch::context_switching
diff --git a/arch/x86_64/src/context_switching/syscall_handler.cpp b/arch/x86_64/src/context_switching/syscall_handler.cpp
new file mode 100644
index 0000000..1bc4ef9
--- /dev/null
+++ b/arch/x86_64/src/context_switching/syscall_handler.cpp
@@ -0,0 +1,20 @@
+#include "arch/context_switching/syscall_handler.hpp"
+
+#include <cstdint>
+
+namespace teachos::arch::context_switching
+{
+  [[gnu::naked]]
+  auto syscall_handler() -> void
+  {
+    uint64_t dummy{};
+    switch (dummy)
+    {
+      case 0:
+        break;
+      default:
+        break;
+    }
+    asm volatile("SYSRET");
+  }
+}  // namespace teachos::arch::context_switching
\ No newline at end of file
diff --git a/arch/x86_64/src/kernel/main.cpp b/arch/x86_64/src/kernel/main.cpp
index 05c879e..e737d44 100644
--- a/arch/x86_64/src/kernel/main.cpp
+++ b/arch/x86_64/src/kernel/main.cpp
@@ -63,6 +63,7 @@ namespace teachos::arch::kernel
     memory::heap::global_heap_allocator::register_heap_allocator(memory::heap::heap_allocator_type::LINKED_LIST);
     // heap_test();
 
+    context_switching::setup_syscall();
     context_switching::switch_to_user_mode();
   }
 }  // namespace teachos::arch::kernel