/* uctx-setjmp.h - setjmp based user-space context switching
 *
 * Copyright (C) 2009 Timo Teräs <timo.teras@iki.fi>
 * All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 or later as
 * published by the Free Software Foundation.
 *
 * See http://www.gnu.org/ for details.
 */

#include <libtf/fiber.h>

#include <stdio.h>
#include <stdlib.h>
#include <setjmp.h>
#ifdef VALGRIND
#include <valgrind/valgrind.h>
#endif

#define STACK_GUARD		0xbad57ac4

struct tf_uctx {
	int *stack_guard;
	void *alloc;
	jmp_buf jmpbuf;
#ifdef VALGRIND
	unsigned int stack_id;
#endif
	struct tf_fiber fiber;
};

#define set_stack(ptr) ({ __asm__("movl %0, %%esp" : : "r"(ptr)); })
#define get_stack() ({ void *ptr; __asm__("movl %%esp, %0" : "=r"(ptr)); ptr; })

attribute_never_inline
static void *tf_uctx_start(tf_fiber_proc fiber_main, size_t private_size)
{
	struct tf_uctx *uctx;

	uctx = alloca(private_size);
	if (setjmp(uctx->jmpbuf) != 0) {
		fiber_main(uctx->fiber.data);
		tf_exit();
	}
	return uctx;
}

static inline
struct tf_fiber *tf_uctx_create(tf_fiber_proc fiber_main, int private_size)
{
	size_t size = TF_STACK_SIZE;
	struct tf_uctx *uctx;
	void *stack, *old_stack, *stack_head, *stack_tail;
#ifdef VALGRIND
	int stack_id;
#endif

	stack = malloc(size);
	if (stack == NULL)
		return NULL;
#ifdef VALGRIND
	stack_id = VALGRIND_STACK_REGISTER(stack, size);
#endif

	/* Assumes stack grows up */
	stack_head = stack + size - 8;
	stack_tail = stack;

	old_stack = get_stack();
	set_stack(stack_head);
	uctx = tf_uctx_start(fiber_main, private_size + sizeof(struct tf_uctx));
	set_stack(old_stack);

#ifdef VALGRIND
	uctx->stack_id = stack_id;
#endif
	uctx->alloc = stack;
	uctx->stack_guard = stack_tail;
	*uctx->stack_guard = STACK_GUARD;

	return &uctx->fiber;
}

static inline
void tf_uctx_destroy(struct tf_fiber *fiber)
{
	struct tf_uctx *uctx = container_of(fiber, struct tf_uctx, fiber);
#ifdef VALGRIND
	VALGRIND_STACK_DEREGISTER(uctx->stack_id);
#endif
	free(uctx->alloc);
}

static inline
int tf_uctx_transfer(struct tf_fiber *from, struct tf_fiber *to, int value)
{
	struct tf_uctx *ufrom = container_of(from, struct tf_uctx, fiber);
	struct tf_uctx *uto   = container_of(to,   struct tf_uctx, fiber);
	int r;

	TF_BUG_ON(unlikely(*ufrom->stack_guard != STACK_GUARD));

	r = setjmp(ufrom->jmpbuf);
	if (r == 0)
		longjmp(uto->jmpbuf, value);
	return r;
}