create trampoline for syscall

3 files changed, 30 insertions, 1 deletions

diff --git a/arch/x86_64/include/arch/boot/pointers.hpp b/arch/x86_64/include/arch/boot/pointers.hpp
index fe9c657..d9a7ab7 100644
--- a/arch/x86_64/include/arch/boot/pointers.hpp
+++ b/arch/x86_64/include/arch/boot/pointers.hpp
@@ -10,6 +10,8 @@ namespace teachos::arch::boot
    */
   extern "C" size_t const multiboot_information_pointer;
 
+  extern "C" void syscall_trampoline();
+
 }  // namespace teachos::arch::boot
 
 #endif  // TEACHOS_ARCH_X86_64_BOOT_POINTERS_HPP
diff --git a/arch/x86_64/src/boot/boot.s b/arch/x86_64/src/boot/boot.s
index 7932045..24b38ca 100644
--- a/arch/x86_64/src/boot/boot.s
+++ b/arch/x86_64/src/boot/boot.s
@@ -352,6 +352,31 @@ 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 faaf831..c949488 100644
--- a/arch/x86_64/src/context_switching/main.cpp
+++ b/arch/x86_64/src/context_switching/main.cpp
@@ -1,5 +1,6 @@
 #include "arch/context_switching/main.hpp"
 
+#include "arch/boot/pointers.hpp"
 #include "arch/exception_handling/assert.hpp"
 #include "arch/kernel/cpu/call.hpp"
 #include "arch/kernel/cpu/control_register.hpp"
@@ -59,7 +60,8 @@ namespace teachos::arch::context_switching
     // People claim that SYSENTER is for 32-Bit, while SYSCALL is for 64-Bit!
 
     // asm volatile("INT $0x80");
-    asm volatile("SYSCALL");
+    // asm volatile("SYSCALL");
+    boot::syscall_trampoline();
 
     video::vga::text::write("Successfully entered user mode!", video::vga::text::common_attributes::green_on_black);
   }