create trampoline for syscall

1 files changed, 25 insertions, 0 deletions

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