1/*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21
22/*
23 * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
24 * Use is subject to license terms.
25 */
26
27/*	Copyright (c) 1988 AT&T	*/
28/*	  All Rights Reserved  	*/
29
30#pragma weak _makecontext = makecontext
31
32#include "lint.h"
33#include <stdarg.h>
34#include <ucontext.h>
35#include <sys/stack.h>
36
37/*
38 * The ucontext_t that the user passes in must have been primed with a
39 * call to getcontext(2), have the uc_stack member set to reflect the
40 * stack which this context will use, and have the uc_link member set
41 * to the context which should be resumed when this context returns.
42 * When makecontext() returns, the ucontext_t will be set to run the
43 * given function with the given parameters on the stack specified by
44 * uc_stack, and which will return to the ucontext_t specified by uc_link.
45 */
46
47/*
48 * The original i386 ABI said that the stack pointer need be only 4-byte
49 * aligned before a function call (STACK_ALIGN == 4).  The ABI supplement
50 * version 1.0 changed the required alignment to 16-byte for the benefit of
51 * floating point code compiled using sse2.  The compiler assumes this
52 * alignment and maintains it for calls it generates.  If the stack is
53 * initially properly aligned, it will continue to be so aligned.  If it is
54 * not initially so aligned, it will never become so aligned.
55 *
56 * One slightly confusing detail to keep in mind is that the 16-byte
57 * alignment (%esp & 0xf == 0) is true just *before* the call instruction.
58 * The call instruction will then push a return value, decrementing %esp by
59 * 4.  Therefore, if one dumps %esp at the at the very first instruction in
60 * a function, it will end with a 0xc.  The compiler expects this and
61 * compensates for it properly.
62 *
63 * Note: If you change this value, you need to change it in the following
64 * files as well:
65 *
66 *  - lib/libc/i386/threads/machdep.c
67 *  - lib/crt/i386/crti.s
68 *  - lib/crt/i386/crt1.s
69 */
70#undef	STACK_ALIGN
71#define	STACK_ALIGN	16
72
73static void resumecontext(void);
74
75void
76makecontext(ucontext_t *ucp, void (*func)(), int argc, ...)
77{
78	long *sp;
79	long *tsp;
80	va_list ap;
81	size_t size;
82
83	ucp->uc_mcontext.gregs[EIP] = (greg_t)func;
84
85	size = sizeof (long) * (argc + 1);
86
87	tsp = (long *)(((uintptr_t)ucp->uc_stack.ss_sp +
88	    ucp->uc_stack.ss_size - size) & ~(STACK_ALIGN - 1));
89
90	/*
91	 * Since we're emulating the call instruction, we must push the
92	 * return address (which involves adjusting the stack pointer to
93	 * have the proper 4-byte bias).
94	 */
95	sp = tsp - 1;
96
97	*sp = (long)resumecontext;		/* return address */
98
99	ucp->uc_mcontext.gregs[UESP] = (greg_t)sp;
100
101	/*
102	 * "push" all the arguments
103	 */
104	va_start(ap, argc);
105	while (argc-- > 0)
106		*tsp++ = va_arg(ap, long);
107	va_end(ap);
108}
109
110
111static void
112resumecontext(void)
113{
114	ucontext_t uc;
115
116	(void) getcontext(&uc);
117	(void) setcontext(uc.uc_link);
118}
119