Kernel: Add bareboness fork() function

kernel/include/kernel/Arch.h

@@ -17,4 +17,8 @@
 	#define read_rsp(rsp) asm volatile("movl %%esp, %0" : "=r"(rsp))
 	#define push_callee_saved() asm volatile("pushal")
 	#define pop_callee_saved() asm volatile("popal")
-#endif
+#endif
+
+#include <stdint.h>
+
+extern "C" uintptr_t read_rip();

kernel/include/kernel/Process.h

@@ -41,6 +41,8 @@ namespace Kernel
 
 		pid_t pid() const { return m_pid; }
 
+		BAN::ErrorOr<Process*> fork(uintptr_t rsp, uintptr_t rip);
+
 		BAN::ErrorOr<int> open(BAN::StringView, int);
 		BAN::ErrorOr<void> close(int fd);
 		BAN::ErrorOr<size_t> read(int fd, void* buffer, size_t count);

kernel/include/kernel/Thread.h

@@ -31,6 +31,8 @@ namespace Kernel
 		static BAN::ErrorOr<Thread*> create_userspace(uintptr_t, Process*, int, char**);
 		~Thread();
 
+		BAN::ErrorOr<Thread*> clone(Process*, uintptr_t rsp, uintptr_t rip);
+
 		pid_t tid() const { return m_tid; }
 
 		void set_rsp(uintptr_t rsp) { m_rsp = rsp; validate_stack(); }