/*      $NetBSD: makecontext.c,v 1.9 2025/04/27 16:15:40 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 1.9 2025/04/27 16:15:40 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;
       int i;
       unsigned long *sp;
       va_list ap;

       /* Compute stack pointer. */
       sp = (unsigned long *)
           ((uintptr_t)ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
       /* Allocate necessary stack space for arguments exceeding a0-5. */
       if (argc > 6)
               sp -= (argc - 6);
       /* Align stack pointer. */
       sp = (unsigned long *)((uintptr_t)sp & ~STACK_ALIGNBYTES);
       gr[_REG_SP] = (__greg_t)sp;
       /* Arrange for return via the trampoline code. */
       gr[_REG_RA] = (__greg_t)__resumecontext;
       gr[_REG_PC] = (__greg_t)func;
       gr[_REG_PV] = (__greg_t)func;

       va_start(ap, argc);
       /* Pass up to six arguments in a0-5. */
       for (i = 0; i < argc && i < 6; i++)
               gr[_REG_A0 + i] = va_arg(ap, unsigned long);
       /* Pass any additional arguments on the stack. */
       for (argc -= i; argc > 0; argc--)
               *sp++ = va_arg(ap, unsigned long);
       va_end(ap);
}