kernel/src/arch/CPU.h

@@ -26,5 +26,7 @@ namespace CPU
     void get_stack_trace_at(Registers* regs, void (*callback)(u64, void*), void* arg);
     void print_stack_trace_at(Registers* regs);
 
+    [[noreturn]] void bootstrap_switch_stack(u64 stack, void* function);
+
     void pause();
 }

kernel/src/arch/x86_64/CPU.cpp

@@ -295,6 +295,15 @@ namespace CPU
             &frame_index);
     }
 
+    [[noreturn]] void bootstrap_switch_stack(u64 stack, void* function)
+    {
+        asm volatile("mov %0, %%rsp\n"
+                     "jmp *%1"
+                     :
+                     : "r"(stack), "r"(function));
+        __builtin_unreachable();
+    }
+
     void pause()
     {
         asm volatile("pause");

kernel/src/main.cpp

@@ -90,11 +90,19 @@ Result<void> init()
     return {};
 }
 
-extern "C" [[noreturn]] void _start()
+[[noreturn]] void init_wrapper()
 {
-    Init::check_magic();
-    Init::early_init();
     auto rc = init();
     if (rc.has_error()) kerrorln("Runtime error: %s", rc.error_string());
     CPU::idle_loop();
 }
+
+// FIXME: Add a guard page to make sure the stack doesn't end up in random kernel memory. Also reclaim this memory after
+// leaving the init task.
+extern "C" [[noreturn]] void _start()
+{
+    Init::check_magic();
+    Init::early_init();
+    Stack stack { MemoryManager::alloc_for_kernel(8, MMU::ReadWrite | MMU::NoExecute).value(), 8 * ARCH_PAGE_SIZE };
+    CPU::bootstrap_switch_stack(stack.top(), (void*)init_wrapper);
+}