Feature: get_stack_pointer (#1214)

* Feature: get_stack_pointer

- all listed arch have been tested by clang
- will be used by linux_clone3_thread
- MSVC is not supported

* fix test

* add precompile fence to stack_pointer.h

* add attribute fence during precompile

* move stack_pointer.h to thread/

- as an internal dependency of linux clone3 thread

* Avoid compile fail, use runtime terminate instead

* fix err msg

Author: SekaiArendelle

include/fast_io_hosted/threads/thread/stack_pointer.h

@@ -0,0 +1,55 @@
+#pragma once
+
+#if defined (_MSC_VER) && !defined(__clang__)
+#error "get_stack_pointer is not supported on MSVC"
+#endif
+
+namespace fast_io::details
+{
+
+/**
+ * @brief Get the stack pointer.
+ * @return void* The stack pointer.
+ *
+ * @note MSVC is not supported.
+ */
+[[nodiscard]]
+#if __has_cpp_attribute(__gnu__::__always_inline__)
+[[__gnu__::__always_inline__]]
+#else
+#error "__gnu__::__always_inline__ is required"
+#endif
+#if __has_cpp_attribute(__gnu__::__artificial__)
+[[__gnu__::__artificial__]]
+#endif
+inline void *get_stack_pointer() noexcept
+{
+	void *result
+#if __has_cpp_attribute(indeterminate)
+		[[indeterminate]]
+#endif
+		;
+
+#if defined(__x86_64__) && !defined(__arm64ec__)
+	__asm__ volatile("movq %%rsp, %0" : "=r"(result));
+#elif defined(__i386__)
+	__asm__ volatile("movl %%esp, %0" : "=r"(result));
+#elif defined(__aarch64__) || defined(__arm64ec__)
+	__asm__ volatile("mov %0, sp" : "=r"(result));
+#elif defined(__arm__)
+	__asm__ volatile("mov %0, sp" : "=r"(result));
+#elif defined(__loongarch__)
+	__asm__ volatile("move %0, $sp" : "=r"(result));
+#elif defined(__riscv)
+	__asm__ volatile("mv %0, sp" : "=r"(result));
+#elif defined(__mips__)
+	__asm__ volatile("move %0, $sp" : "=r"(result));
+#elif defined(__powerpc__)
+	__asm__ volatile("mr %0, 1" : "=r"(result));
+#else
+    ::fast_io::fast_terminate();
+#endif
+	return result;
+}
+
+} // namespace fast_io