makecontext.c revision 1.3 
1/*	$NetBSD: makecontext.c,v 1.3 2008/04/28 20:22:57 martin Exp $	*/
2
3/*-
4 * Copyright (c) 2003 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Matt Thomas.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
29 * POSSIBILITY OF SUCH DAMAGE.
30 */
31
32#include <sys/cdefs.h>
33#if defined(LIBC_SCCS) && !defined(lint)
34__RCSID("$NetBSD: makecontext.c,v 1.3 2008/04/28 20:22:57 martin Exp $");
35#endif
36
37#include <stddef.h>
38#include <inttypes.h>
39#include <ucontext.h>
40#include "extern.h"
41
42#include <stdarg.h>
43
44void
45makecontext(ucontext_t *ucp, void (*func)(void), int argc, ...)
46{
47	__greg_t *gr = ucp->uc_mcontext.__gregs;
48	va_list ap;
49	int *sp;
50	int i;
51
52	/* Compute and align stack pointer. */
53	sp = (int *)
54	    (((uintptr_t)ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size) & ~0x3);
55
56	/*
57	 * Allocate necessary stack space for arguments including arg count
58	 * and call frame
59	 */
60	sp -= argc + 1 + 5;
61
62	va_start(ap, argc);
63	sp[5] = argc;
64	for (i = 1; argc > 0; argc--, i++)
65		sp[5 + i] = va_arg(ap, int);
66	va_end(ap);
67
68	sp[0] = 0;			/* condition handler is null */
69	sp[1] = 0x20000000;		/* make this a CALLS frame */
70	sp[2] = 0;			/* saved argument pointer */
71	sp[3] = 0;			/* saved frame pointer */
72	sp[4] = (int)_resumecontext+2;	/* return via trampoline code */
73
74	gr[_REG_AP] = (__greg_t)(sp + 5);
75	gr[_REG_SP] = (__greg_t)sp;
76	gr[_REG_FP] = (__greg_t)sp;
77	gr[_REG_PC] = (__greg_t)func+2;
78
79}
80