/*      $NetBSD: makecontext.c,v 1.4 2012/03/21 14:03:06 christos Exp $ */

/*-
 * Copyright (c) 2001 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Klaus Klein.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: makecontext.c,v 1.4 2012/03/21 14:03:06 christos Exp $");
#endif

#include <stddef.h>
#include <inttypes.h>
#include <ucontext.h>
#include "extern.h"

#include <stdarg.h>

void
makecontext(ucontext_t *ucp, void (*func)(void), int argc, ...)
{
        __greg_t *gr = ucp->uc_mcontext.__gregs;
        int i;
        unsigned int *sp;
        va_list ap;

        /* Compute and align stack pointer. */
        sp = (unsigned int *)
            (((uintptr_t)ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size) & ~7);
        /* Allocate necessary stack space for arguments exceeding r0-3. */
        if (argc > 4)
                sp -= argc - 4;
        gr[_REG_SP] = (__greg_t)(uintptr_t)sp;
        /* Wipe out frame pointer. */
        gr[_REG_FP] = 0;
        /* Arrange for return via the trampoline code. */
        gr[_REG_LR] = (__greg_t)(uintptr_t)_resumecontext;
        gr[_REG_PC] = (__greg_t)(uintptr_t)func;

        va_start(ap, argc);
        /* Pass up to four arguments in r0-3. */
        for (i = 0; i < argc && i < 4; i++)
                gr[_REG_R0 + i] = va_arg(ap, int);
        /* Pass any additional arguments on the stack. */
        for (argc -= i; argc > 0; argc--)
                *sp++ = va_arg(ap, int);
        va_end(ap);
}