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 /*
31 * Copyright 2023 Oxide Computer Company
32 */
33
34 #pragma weak _makecontext = makecontext
35
36 #include "lint.h"
37 #include <stdarg.h>
38 #include <ucontext.h>
39 #include <sys/stack.h>
40 #include <sys/auxv.h>
41 #include <errno.h>
42 #include "libc.h"
43
44 /*
45 * The ucontext_t that the user passes in must have been primed with a
46 * call to getcontext(2), have the uc_stack member set to reflect the
47 * stack which this context will use, and have the uc_link member set
48 * to the context which should be resumed when this context returns.
49 * When makecontext() returns, the ucontext_t will be set to run the
50 * given function with the given parameters on the stack specified by
51 * uc_stack, and which will return to the ucontext_t specified by uc_link.
52 */
53
54 /*
55 * The original i386 ABI said that the stack pointer need be only 4-byte
56 * aligned before a function call (STACK_ALIGN == 4). The ABI supplement
57 * version 1.0 changed the required alignment to 16-byte for the benefit of
58 * floating point code compiled using sse2. The compiler assumes this
59 * alignment and maintains it for calls it generates. If the stack is
60 * initially properly aligned, it will continue to be so aligned. If it is
61 * not initially so aligned, it will never become so aligned.
62 *
63 * One slightly confusing detail to keep in mind is that the 16-byte
64 * alignment (%esp & 0xf == 0) is true just *before* the call instruction.
65 * The call instruction will then push a return value, decrementing %esp by
66 * 4. Therefore, if one dumps %esp at the at the very first instruction in
67 * a function, it will end with a 0xc. The compiler expects this and
68 * compensates for it properly.
69 *
70 * Note: If you change this value, you need to change it in the following
71 * files as well:
72 *
73 * - lib/libc/i386/threads/machdep.c
74 * - lib/crt/i386/crti.s
75 * - lib/crt/i386/crt1.s
76 */
77 #undef STACK_ALIGN
78 #define STACK_ALIGN 16
79
80 static void resumecontext(void);
81
82 void
83 makecontext(ucontext_t *ucp, void (*func)(), int argc, ...)
84 {
85 long *sp;
86 long *tsp;
87 va_list ap;
88 size_t size;
89
90 ucp->uc_mcontext.gregs[EIP] = (greg_t)func;
91
92 size = sizeof (long) * (argc + 1);
93
94 tsp = (long *)(((uintptr_t)ucp->uc_stack.ss_sp +
95 ucp->uc_stack.ss_size - size) & ~(STACK_ALIGN - 1));
96
97 /*
98 * Since we're emulating the call instruction, we must push the
99 * return address (which involves adjusting the stack pointer to
100 * have the proper 4-byte bias).
101 */
102 sp = tsp - 1;
103
104 *sp = (long)resumecontext; /* return address */
105
106 ucp->uc_mcontext.gregs[UESP] = (greg_t)sp;
107
108 /*
109 * "push" all the arguments
110 */
111 va_start(ap, argc);
112 while (argc-- > 0)
113 *tsp++ = va_arg(ap, long);
114 va_end(ap);
115 }
116
117
118 static void
119 resumecontext(void)
120 {
121 ucontext_t uc;
122
123 (void) getcontext(&uc);
124 (void) setcontext(uc.uc_link);
125 }
126
127 /*
128 * This is the ISA-specific allocation logic for allocating and setting up an
129 * extended ucontext_t. In particular, right now we need to allocate and add
130 * space for the UC_XSAVE member if we have the appropriate hardware support.
131 * The i386 / amd64 versions could be consolidated in a single x86 impl, but we
132 * don't have that right now.
133 */
134 ucontext_t *
135 ucontext_alloc(uint32_t flags)
136 {
137 boolean_t do_xsave = B_FALSE;
138 size_t to_alloc = sizeof (ucontext_t);
139 ucontext_t *ucp;
140
141 if (flags != 0) {
142 errno = EINVAL;
143 return (NULL);
144 }
145
146 /*
147 * This value isn't really 100% accurate. The xsave size is basically
148 * the worst case that we can have. The XMM / xsave structures aren't
149 * included in here, but are going to be enough to cover this. We can
150 * probably try to do a little better and should consider asking the
151 * kernel for something more accurate. In particular, the problem with
152 * tis is that it doesn't account for the right size of future-looking
153 * dynamic things, but then again neither does rtld. We'll deal with
154 * this when we have support for the xfd MSR and actually use it. For
155 * more information see uts/intel/os/fpu.c's big theory statement.
156 */
157 switch (___getauxval(AT_SUN_FPTYPE)) {
158 case AT_386_FPINFO_XSAVE:
159 case AT_386_FPINFO_XSAVE_AMD:
160 do_xsave = B_TRUE;
161 to_alloc += ___getauxval(AT_SUN_FPSIZE);
162 break;
163 default:
164 break;
165 }
166
167 ucp = calloc(1, to_alloc);
168 if (ucp == NULL) {
169 return (NULL);
170 }
171
172 if (do_xsave) {
173 uintptr_t addr = (uintptr_t)ucp;
174 ucp->uc_xsave = addr + sizeof (ucontext_t);
175 }
176
177 return (ucp);
178 }
179
180 void
181 ucontext_free(ucontext_t *ucp)
182 {
183 free(ucp);
184 }