/*      $NetBSD: makecontext.c,v 1.4 2009/07/30 20:57:17 dsl Exp $      */

/*-
 * Copyright (c) 1999 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.
 *
 * Modified from the i386 version for x86_64 by fvdl@wasabisystems.com.
 *
 */

#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: makecontext.c,v 1.4 2009/07/30 20:57:17 dsl Exp $");
#endif

#include <inttypes.h>
#include <stddef.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;
        uintptr_t *sp;
        va_list ap;
        int stackargs, i;

        stackargs = argc - 6;

        /* LINTED __greg_t is safe */
        gr[_REG_RIP] = (__greg_t)func;

        /* LINTED uintptr_t is safe */
        sp  = (uintptr_t *)
            ((uintptr_t)ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);

        /* LINTED uintptr_t is safe */
        sp  = (uintptr_t *)(((uintptr_t)sp & ~15));
        sp--;
        if (stackargs > 0)
                sp -= stackargs;
        /* LINTED __greg_t is safe */
        gr[_REG_RSP] = (__greg_t)sp;
        gr[_REG_RBP] = (__greg_t)0;     /* Wipe out frame pointer. */

        /* Put return address on top of stack. */
        /* LINTED uintptr_t is safe */
        *sp++ = (uintptr_t)_resumecontext;

        /*
         * Construct argument list.
         * The registers used to pass the first 6 arguments
         * (rdi, rsi, rdx, rcx, r8, r9) are the first 6 in gregs,
         * in that order, so those arguments can just be copied to
         * the gregs array.
         */
        va_start(ap, argc);
        for (i = 0; i < 6 && argc > 0; i++) {
                argc--;
                /* LINTED __greg_t is safe */
                gr[i] = va_arg(ap, __greg_t);
        }

        while (stackargs-- > 0) {
                /* LINTED uintptr_t is safe */
                *sp++ = va_arg(ap, uintptr_t);
        }

        va_end(ap);
}