/* Copyright (C) 2021,2022 fef <owo@fef.moe>.  All rights reserved. */

#pragma once

#include <arch/page.h>
#include <arch/sched.h>

#include <gay/cdefs.h>
#include <gay/config.h>
#include <gay/types.h>

static inline int smp_cpuid(void)
{
#if CFG_SMP
	/*
	 * The x86 has a dedicated CPUID instruction that can be used to query
	 * pretty much anything except literally the cpu id.  Therefore, we make
	 * use of the fact that kernel stacks are always aligned to their size.
	 * The cpu number is the topmost item on the stack; for cpu 0 this gets
	 * pushed in the assembly routine in startup{32,64}.S and for all others
	 * ... there is no implementation yet.
	 */
	u_register_t sp;

#ifdef __x86_64__
	__asm__ volatile("movq %%rsp, %0" : "=r"(sp));
#else
	__asm__ volatile("movl %%esp, %0" : "=r"(sp));
#endif

	sp &= ~(KERN_STACK_SIZE - 1);
	return ((int *)sp)[KERN_STACK_SIZE / sizeof(int) - 1];
#else /* !CFG_SMP */
	return 0;
#endif /* !CFG_SMP */
}