Wireframe for syscalls in place

zion/syscall/syscall.cpp

@@ -0,0 +1,57 @@
+#include "syscall/syscall.h"
+
+#include <stdint.h>
+
+#include "debug/debug.h"
+#include "scheduler/scheduler.h"
+
+#define EFER 0xC0000080
+#define STAR 0xC0000081
+#define LSTAR 0xC0000082
+
+namespace {
+
+uint64_t GetMSR(uint32_t msr) {
+  uint32_t lo, hi;
+  asm("rdmsr" : "=a"(lo), "=d"(hi) : "c"(msr));
+  return (static_cast<uint64_t>(hi) << 32) | lo;
+}
+
+void SetMSR(uint32_t msr, uint64_t val) {
+  uint32_t lo = static_cast<uint32_t>(val);
+  uint32_t hi = val >> 32;
+  asm("wrmsr" ::"a"(lo), "d"(hi), "c"(msr));
+}
+
+extern "C" void syscall_enter();
+
+}  // namespace
+
+// Used by syscall_enter.s
+extern "C" uint64_t GetKernelRsp() {
+  return sched::CurrentThread().Rsp0Start();
+}
+
+void InitSyscall() {
+  uint64_t efer_val = GetMSR(EFER);
+  efer_val |= 1;
+  SetMSR(EFER, efer_val);
+  if (GetMSR(EFER) != efer_val) {
+    panic("Failed to set EFER MSR");
+  }
+
+  uint64_t star_val = GetMSR(STAR);
+  // FIXME: Fix GDT such that we can properly set the user CS.
+  // Due to the ability to jump from a 64 bit kernel into compatibility mode,
+  // we set the user_cs to the kernel_cs because it adds 16 to jump to 64-bit
+  // mode. See AMD Manual 3.4 instruction SYSRET for more info.
+  uint64_t kernel_cs = 0x8;
+  uint64_t user_cs = kernel_cs;
+  star_val |= (kernel_cs << 32) | (user_cs << 48);
+  SetMSR(STAR, star_val);
+  SetMSR(LSTAR, reinterpret_cast<uint64_t>(syscall_enter));
+}
+
+extern "C" void SyscallHandler(uint64_t call_id, char* message) {
+  dbgln(message);
+}