1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
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/types.h>
30 #include <sys/ucontext.h>
31 #include <stdarg.h>
32 #include <stdlib.h>
33
34 typedef void (*func_t)(uint64_t, uint64_t, uint64_t, uint64_t, uint64_t,
35 uint64_t);
36
37 /* Prototypes */
38 static void makectx_wrapper(ucontext_t *ucp, func_t func, uint64_t *args);
39
40 __weak_reference(__makecontext, makecontext);
41
42 void
__makecontext(ucontext_t * ucp,void (* start)(void),int argc,...)43 __makecontext(ucontext_t *ucp, void (*start)(void), int argc, ...)
44 {
45 uint64_t *args;
46 uint64_t *sp;
47 va_list ap;
48 int i;
49
50 /* A valid context is required. */
51 if ((ucp == NULL) || (ucp->uc_mcontext.mc_len != sizeof(mcontext_t)))
52 return;
53 else if ((argc < 0) || (argc > 6) || (ucp->uc_stack.ss_sp == NULL) ||
54 (ucp->uc_stack.ss_size < MINSIGSTKSZ)) {
55 /*
56 * This should really return -1 with errno set to ENOMEM
57 * or something, but the spec says that makecontext is
58 * a void function. At least make sure that the context
59 * isn't valid so it can't be used without an error.
60 */
61 ucp->uc_mcontext.mc_len = 0;
62 return;
63 }
64
65 /* Align the stack to 16 bytes. */
66 sp = (uint64_t *)(ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
67 sp = (uint64_t *)((uint64_t)sp & ~15UL);
68
69 /* Allocate space for a maximum of 6 arguments on the stack. */
70 args = sp - 6;
71
72 /*
73 * Account for arguments on stack and do the funky C entry alignment.
74 * This means that we need an 8-byte-odd alignment since the ABI expects
75 * the return address to be pushed, thus breaking the 16 byte alignment.
76 */
77 sp -= 7;
78
79 /* Add the arguments: */
80 va_start(ap, argc);
81 for (i = 0; i < argc; i++)
82 args[i] = va_arg(ap, uint64_t);
83 va_end(ap);
84 for (i = argc; i < 6; i++)
85 args[i] = 0;
86
87 ucp->uc_mcontext.mc_rdi = (register_t)ucp;
88 ucp->uc_mcontext.mc_rsi = (register_t)start;
89 ucp->uc_mcontext.mc_rdx = (register_t)args;
90 ucp->uc_mcontext.mc_rbp = 0;
91 ucp->uc_mcontext.mc_rbx = (register_t)sp;
92 ucp->uc_mcontext.mc_rsp = (register_t)sp;
93 ucp->uc_mcontext.mc_rip = (register_t)makectx_wrapper;
94 }
95
96 static void
makectx_wrapper(ucontext_t * ucp,func_t func,uint64_t * args)97 makectx_wrapper(ucontext_t *ucp, func_t func, uint64_t *args)
98 {
99 (*func)(args[0], args[1], args[2], args[3], args[4], args[5]);
100 if (ucp->uc_link == NULL)
101 exit(0);
102 setcontext((const ucontext_t *)ucp->uc_link);
103 /* should never get here */
104 abort();
105 /* NOTREACHED */
106 }
107