1/*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright (c) 2004 Suleiman Souhlal
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 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29#include <sys/cdefs.h>
30__FBSDID("$FreeBSD$");
31
32#include <sys/param.h>
33
34#include <stdarg.h>
35#include <stdlib.h>
36#include <unistd.h>
37#include <stdio.h>
38#include <ucontext.h>
39
40__weak_reference(__makecontext, makecontext);
41
42void _ctx_done(ucontext_t *ucp);
43void _ctx_start(void);
44
45void
46_ctx_done(ucontext_t *ucp)
47{
48	if (ucp->uc_link == NULL)
49		exit(0);
50	else {
51		/* invalidate context */
52		ucp->uc_mcontext.mc_len = 0;
53
54		setcontext((const ucontext_t *)ucp->uc_link);
55
56		abort(); /* should never return from above call */
57	}
58}
59
60void
61__makecontext(ucontext_t *ucp, void (*start)(void), int argc, ...)
62{
63	mcontext_t *mc;
64	char *sp;
65	va_list ap;
66	int i, regargs, stackargs;
67
68	/* Sanity checks */
69	if ((ucp == NULL) || (argc < 0)
70	    || (ucp->uc_stack.ss_sp == NULL)
71	    || (ucp->uc_stack.ss_size < MINSIGSTKSZ)) {
72		/* invalidate context */
73		ucp->uc_mcontext.mc_len = 0;
74		return;
75	}
76
77	/*
78	 * The stack must have space for the frame pointer, saved
79	 * link register, overflow arguments, and be 16-byte
80	 * aligned.
81	 */
82	stackargs = (argc > 8) ? argc - 8 : 0;
83	sp = (char *) ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size
84		- sizeof(uintptr_t)*(stackargs + 2);
85	sp = (char *)((uintptr_t)sp & ~0x1f);
86
87	mc = &ucp->uc_mcontext;
88
89	/*
90	 * Up to 8 register args. Assumes all args are 64-bit and
91	 * integer only. Not sure how to cater for floating point.
92	 */
93	regargs = (argc > 8) ? 8 : argc;
94	va_start(ap, argc);
95	for (i = 0; i < regargs; i++)
96		mc->mc_gpr[3 + i] = va_arg(ap, uint64_t);
97
98	/*
99	 * Overflow args go onto the stack
100	 */
101	if (argc > 8) {
102		uint64_t *argp;
103
104		/* Skip past frame pointer and saved LR */
105#if !defined(_CALL_ELF) || _CALL_ELF == 1
106		argp = (uint64_t *)sp + 6;
107#else
108		argp = (uint64_t *)sp + 4;
109#endif
110
111		for (i = 0; i < stackargs; i++)
112			*argp++ = va_arg(ap, uint64_t);
113	}
114	va_end(ap);
115
116	/*
117	 * Use caller-saved regs 14/15 to hold params that _ctx_start
118	 * will use to invoke the user-supplied func
119	 */
120#if !defined(_CALL_ELF) || _CALL_ELF == 1
121	/* Cast to ensure this is treated as a function descriptor. */
122	mc->mc_srr0 = *(uintptr_t *)_ctx_start;
123#else
124	mc->mc_srr0 = (uintptr_t) _ctx_start;
125#endif
126	mc->mc_gpr[1] = (uintptr_t) sp;		/* new stack pointer */
127	mc->mc_gpr[14] = (uintptr_t) start;	/* r14 <- start */
128	mc->mc_gpr[15] = (uintptr_t) ucp;	/* r15 <- ucp */
129}
130