user: implement mlibc as the libc, finally.

It's finally done..

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

user/include/mlibc/sysdeps/linux/generic/thread.cpp

@@ -0,0 +1,60 @@
+#include <mlibc/thread-entry.hpp>
+#include <mlibc/all-sysdeps.hpp>
+#include <mlibc/thread.hpp>
+#include <bits/ensure.h>
+#include <sys/mman.h>
+#include <stdint.h>
+#include <stddef.h>
+#include <errno.h>
+
+extern "C" void __mlibc_enter_thread(void *entry, void *user_arg) {
+	// The linux kernel already sets the TCB in sys_clone().
+	auto tcb = mlibc::get_current_tcb();
+
+	// Wait until our parent sets up the TID.
+	while(!__atomic_load_n(&tcb->tid, __ATOMIC_RELAXED))
+		mlibc::sys_futex_wait(&tcb->tid, 0, nullptr);
+
+	tcb->invokeThreadFunc(entry, user_arg);
+
+	__atomic_store_n(&tcb->didExit, 1, __ATOMIC_RELEASE);
+	mlibc::sys_futex_wake(&tcb->didExit);
+
+	mlibc::sys_thread_exit();
+}
+
+namespace mlibc {
+
+static constexpr size_t default_stacksize = 0x200000;
+
+int sys_prepare_stack(void **stack, void *entry, void *user_arg, void *tcb, size_t *stack_size, size_t *guard_size, void **stack_base) {
+	(void)tcb;
+	if (!*stack_size)
+		*stack_size = default_stacksize;
+
+	uintptr_t map;
+	if (*stack) {
+		map = reinterpret_cast<uintptr_t>(*stack);
+		*guard_size = 0;
+	} else {
+		map = reinterpret_cast<uintptr_t>(
+				mmap(nullptr, *stack_size + *guard_size,
+					PROT_NONE,
+					MAP_PRIVATE | MAP_ANONYMOUS, -1, 0)
+				);
+		if (reinterpret_cast<void*>(map) == MAP_FAILED)
+			return EAGAIN;
+		int ret = mprotect(reinterpret_cast<void*>(map + *guard_size), *stack_size,
+				PROT_READ | PROT_WRITE);
+		if(ret)
+			return EAGAIN;
+	}
+
+	*stack_base = reinterpret_cast<void*>(map);
+	auto sp = reinterpret_cast<uintptr_t*>(map + *guard_size + *stack_size);
+	*--sp = reinterpret_cast<uintptr_t>(user_arg);
+	*--sp = reinterpret_cast<uintptr_t>(entry);
+	*stack = reinterpret_cast<void*>(sp);
+	return 0;
+}
+} // namespace mlibc