/*      $NetBSD: makecontext.c,v 1.10 2025/04/24 23:54:13 riastradh 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 1.10 2025/04/24 23:54:13 riastradh Exp $");
#endif

#include <sys/param.h>

#include <inttypes.h>
#include <stdarg.h>
#include <stddef.h>
#include <ucontext.h>

#include "extern.h"

void __resumecontext(void) __dead;

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

        /* LINTED uintptr_t is safe */
        sp  = (__greg_t *)
            ((uintptr_t)ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
#if defined(__mips_o32) || defined(__mips_o64)
        sp -= (argc >= 4 ? argc : 4);   /* Make room for >=4 arguments. */
#elif defined(__mips_n32) || defined(__mips_n64)
        sp -= (argc > 8 ? argc - 8 : 0); /* Make room for > 8 arguments. */
#endif
        /* LINTED uintptr_t is safe */
        sp  = (__greg_t *)((uintptr_t)sp & ~STACK_ALIGNBYTES);

        gr[_REG_SP]  = (intptr_t)sp;
        gr[_REG_RA]  = (intptr_t)__resumecontext;
        gr[_REG_T9]  = (intptr_t)func;          /* required for .abicalls */
        gr[_REG_EPC] = (intptr_t)func;

        /* Construct argument list. */
        va_start(ap, argc);
#if defined(__mips_o32) || defined(__mips_o64)
        /* Up to the first four arguments are passed in $a0-3. */
        for (i = 0; i < argc && i < 4; i++)
                /* LINTED __greg_t is safe */
                gr[_REG_A0 + i] = va_arg(ap, __greg_t);
        /* Pass remaining arguments on the stack above the $a0-3 gap. */
        sp += i;
#endif
#if defined(__mips_n32) || defined(__mips_n64)
        /* Up to the first 8 arguments are passed in $a0-7. */
        for (i = 0; i < argc && i < 8; i++)
                /* LINTED __greg_t is safe */
                gr[_REG_A0 + i] = va_arg(ap, __greg_t);
        /* Pass remaining arguments on the stack */
#endif
        for (; i < argc; i++)
                /* LINTED uintptr_t is safe */
                *sp++ = va_arg(ap, __greg_t);
        va_end(ap);
}