makecontext.c revision 331722 
1/*
2 * Copyright (c) 2003 Marcel Moolenaar
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *
9 * 1. Redistributions of source code must retain the above copyright
10 *    notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 *    notice, this list of conditions and the following disclaimer in the
13 *    documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27#include <sys/cdefs.h>
28__FBSDID("$FreeBSD: stable/11/lib/libc/amd64/gen/makecontext.c 331722 2018-03-29 02:50:57Z eadler $");
29
30#include <sys/types.h>
31#include <sys/ucontext.h>
32#include <stdarg.h>
33#include <stdlib.h>
34
35typedef void (*func_t)(uint64_t, uint64_t, uint64_t, uint64_t, uint64_t,
36    uint64_t);
37
38/* Prototypes */
39static void makectx_wrapper(ucontext_t *ucp, func_t func, uint64_t *args);
40
41__weak_reference(__makecontext, makecontext);
42
43void
44__makecontext(ucontext_t *ucp, void (*start)(void), int argc, ...)
45{
46	uint64_t *args;
47	uint64_t *sp;
48	va_list ap;
49	int i;
50
51	/* A valid context is required. */
52	if ((ucp == NULL) || (ucp->uc_mcontext.mc_len != sizeof(mcontext_t)))
53		return;
54	else if ((argc < 0) || (argc > 6) || (ucp->uc_stack.ss_sp == NULL) ||
55	    (ucp->uc_stack.ss_size < MINSIGSTKSZ)) {
56		/*
57		 * This should really return -1 with errno set to ENOMEM
58		 * or something, but the spec says that makecontext is
59		 * a void function.   At least make sure that the context
60		 * isn't valid so it can't be used without an error.
61		 */
62		ucp->uc_mcontext.mc_len = 0;
63		return;
64	}
65
66	/* Align the stack to 16 bytes. */
67	sp = (uint64_t *)(ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
68	sp = (uint64_t *)((uint64_t)sp & ~15UL);
69
70	/* Allocate space for a maximum of 6 arguments on the stack. */
71	args = sp - 6;
72
73	/*
74	 * Account for arguments on stack and do the funky C entry alignment.
75	 * This means that we need an 8-byte-odd alignment since the ABI expects
76	 * the return address to be pushed, thus breaking the 16 byte alignment.
77	 */
78	sp -= 7;
79
80	/* Add the arguments: */
81	va_start(ap, argc);
82	for (i = 0; i < argc; i++)
83		args[i] = va_arg(ap, uint64_t);
84	va_end(ap);
85	for (i = argc; i < 6; i++)
86		args[i] = 0;
87
88	ucp->uc_mcontext.mc_rdi = (register_t)ucp;
89	ucp->uc_mcontext.mc_rsi = (register_t)start;
90	ucp->uc_mcontext.mc_rdx = (register_t)args;
91	ucp->uc_mcontext.mc_rbp = 0;
92	ucp->uc_mcontext.mc_rbx = (register_t)sp;
93	ucp->uc_mcontext.mc_rsp = (register_t)sp;
94	ucp->uc_mcontext.mc_rip = (register_t)makectx_wrapper;
95}
96
97static void
98makectx_wrapper(ucontext_t *ucp, func_t func, uint64_t *args)
99{
100	(*func)(args[0], args[1], args[2], args[3], args[4], args[5]);
101	if (ucp->uc_link == NULL)
102		exit(0);
103	setcontext((const ucontext_t *)ucp->uc_link);
104	/* should never get here */
105	abort();
106	/* NOTREACHED */
107}
108