makecontext.c revision 330897 
1/*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright (c) 2003 Marcel Moolenaar
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 *
11 * 1. Redistributions of source code must retain the above copyright
12 *    notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
18 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
19 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
20 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
21 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
22 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
26 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 */
28
29#include <sys/cdefs.h>
30__FBSDID("$FreeBSD: stable/11/lib/libc/amd64/gen/makecontext.c 330897 2018-03-14 03:19:51Z eadler $");
31
32#include <sys/types.h>
33#include <sys/ucontext.h>
34#include <stdarg.h>
35#include <stdlib.h>
36
37typedef void (*func_t)(uint64_t, uint64_t, uint64_t, uint64_t, uint64_t,
38    uint64_t);
39
40/* Prototypes */
41static void makectx_wrapper(ucontext_t *ucp, func_t func, uint64_t *args);
42
43__weak_reference(__makecontext, makecontext);
44
45void
46__makecontext(ucontext_t *ucp, void (*start)(void), int argc, ...)
47{
48	uint64_t *args;
49	uint64_t *sp;
50	va_list ap;
51	int i;
52
53	/* A valid context is required. */
54	if ((ucp == NULL) || (ucp->uc_mcontext.mc_len != sizeof(mcontext_t)))
55		return;
56	else if ((argc < 0) || (argc > 6) || (ucp->uc_stack.ss_sp == NULL) ||
57	    (ucp->uc_stack.ss_size < MINSIGSTKSZ)) {
58		/*
59		 * This should really return -1 with errno set to ENOMEM
60		 * or something, but the spec says that makecontext is
61		 * a void function.   At least make sure that the context
62		 * isn't valid so it can't be used without an error.
63		 */
64		ucp->uc_mcontext.mc_len = 0;
65		return;
66	}
67
68	/* Align the stack to 16 bytes. */
69	sp = (uint64_t *)(ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
70	sp = (uint64_t *)((uint64_t)sp & ~15UL);
71
72	/* Allocate space for a maximum of 6 arguments on the stack. */
73	args = sp - 6;
74
75	/*
76	 * Account for arguments on stack and do the funky C entry alignment.
77	 * This means that we need an 8-byte-odd alignment since the ABI expects
78	 * the return address to be pushed, thus breaking the 16 byte alignment.
79	 */
80	sp -= 7;
81
82	/* Add the arguments: */
83	va_start(ap, argc);
84	for (i = 0; i < argc; i++)
85		args[i] = va_arg(ap, uint64_t);
86	va_end(ap);
87	for (i = argc; i < 6; i++)
88		args[i] = 0;
89
90	ucp->uc_mcontext.mc_rdi = (register_t)ucp;
91	ucp->uc_mcontext.mc_rsi = (register_t)start;
92	ucp->uc_mcontext.mc_rdx = (register_t)args;
93	ucp->uc_mcontext.mc_rbp = 0;
94	ucp->uc_mcontext.mc_rbx = (register_t)sp;
95	ucp->uc_mcontext.mc_rsp = (register_t)sp;
96	ucp->uc_mcontext.mc_rip = (register_t)makectx_wrapper;
97}
98
99static void
100makectx_wrapper(ucontext_t *ucp, func_t func, uint64_t *args)
101{
102	(*func)(args[0], args[1], args[2], args[3], args[4], args[5]);
103	if (ucp->uc_link == NULL)
104		exit(0);
105	setcontext((const ucontext_t *)ucp->uc_link);
106	/* should never get here */
107	abort();
108	/* NOTREACHED */
109}
110