/*      $NetBSD: _lwp.c,v 1.4 2023/04/02 07:26:18 skrll Exp $   */

/*-
 * Copyright (c) 2009 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Christos Zoulas
 *
 * 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: _lwp.c,v 1.4 2023/04/02 07:26:18 skrll Exp $");
#endif /* LIBC_SCCS and not lint */

#include "namespace.h"
#include <sys/types.h>
#include <inttypes.h>
#include <ucontext.h>
#include <lwp.h>
#include <stdlib.h>

void
_lwp_makecontext(ucontext_t *u, void (*start)(void *),
    void *arg, void *private, caddr_t stack_base, size_t stack_size)
{
        __greg_t *gr = u->uc_mcontext.__gregs;
        int *sp;

        getcontext(u);
        u->uc_link = NULL;

        u->uc_stack.ss_sp = stack_base;
        u->uc_stack.ss_size = stack_size;

        /* Align to a word */
        /* LINTED uintptr_t is safe */
        sp = (int *)((uintptr_t)(stack_base + stack_size) & ~0x3);

        /*
         * Allocate necessary stack space for arguments including arg count
         * and call frame
         */
        sp -= 1 + 1 + 5;

        sp[0] = 0;                      /* condition handler is null */
        sp[1] = 0x20000000;             /* make this a CALLS frame */
        sp[2] = 0;                      /* saved argument pointer */
        sp[3] = 0;                      /* saved frame pointer */
        sp[4] = (int)(uintptr_t)_lwp_exit + 2;/* return via _lwp_exit */
        sp[5] = 1;                      /* argc */
        sp[6] = (int)(uintptr_t)arg;            /* argv */

        gr[_REG_AP] = (__greg_t)(uintptr_t)(sp + 5);
        gr[_REG_SP] = (__greg_t)(uintptr_t)sp;
        gr[_REG_FP] = (__greg_t)(uintptr_t)sp;
        gr[_REG_PC] = (__greg_t)(uintptr_t)start + 2;

        /*
         * Push the TLS pointer onto the new stack also.
         * The _UC_TLSBASE flag tells the kernel to pop it and use it.
         */
        *--sp = (int)(intptr_t)private;
        gr[_REG_SP] = (__greg_t)(uintptr_t)sp;
        u->uc_flags |= _UC_TLSBASE;
}