First Hello world syscall

kernel/amd64/syscall.c

@@ -0,0 +1,19 @@
+#include <amd64/gdt.h>
+#include <amd64/intr.h>
+#include <amd64/msr-index.h>
+#include <amd64/msr.h>
+#include <sys/debug.h>
+
+extern void amd64_syscall_entry (void);
+
+void amd64_syscall_dispatch (void* stack_ptr) {
+  struct saved_regs* regs = stack_ptr;
+  DEBUG ("hello syscall\n");
+}
+
+void syscall_init (void) {
+  amd64_wrmsr (MSR_STAR, ((uint64_t)GDT_KCODE << 32) | ((uint64_t)(GDT_UCODE - 16) << 48));
+  amd64_wrmsr (MSR_LSTAR, (uint64_t)&amd64_syscall_entry);
+  amd64_wrmsr (MSR_SYSCALL_MASK, (1ULL << 9));
+  amd64_wrmsr (MSR_EFER, amd64_rdmsr (MSR_EFER) | EFER_SCE);
+}