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
makecontext(ucontext_t * ucp,void (* func)(),int argc,...)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
resumecontext(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, we need to allocate and add space for the
130 * UC_XSAVE member if we have the appropriate hardware support. The i386 /
131 * amd64 versions could be consolidated in a single x86 impl, but we don't have
132 * that yet.
133 */
134 ucontext_t *
ucontext_alloc(uint32_t flags)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 * The AT_SUN_FPTYPE value is used as an approximation for the size of
148 * the uc_xsave structure that we need additional space for. Ideally we
149 * should ask the kernel how much space we actually need and only
150 * allocate that much. Because the uc_xsave member does not need to
151 * include the 512-byte XMM structure or the full xsave header, this
152 * will work in the interim.
153 *
154 * Currently the system doesn't support dynamically enabling FPU
155 * features with the Intel xfd (extended feature disable) MSR. When we
156 * have support for that we'll need to redo this and ask the kernel for
157 * the right size. We will probably want to cache the size for rtld as
158 * well. For more information see uts/intel/os/fpu.c's big theory
159 * statement.
160 */
161 switch (___getauxval(AT_SUN_FPTYPE)) {
162 case AT_386_FPINFO_XSAVE:
163 case AT_386_FPINFO_XSAVE_AMD:
164 do_xsave = B_TRUE;
165 to_alloc += ___getauxval(AT_SUN_FPSIZE);
166 break;
167 default:
168 break;
169 }
170
171 ucp = calloc(1, to_alloc);
172 if (ucp == NULL) {
173 return (NULL);
174 }
175
176 if (do_xsave) {
177 uintptr_t addr = (uintptr_t)ucp;
178 ucp->uc_xsave = addr + sizeof (ucontext_t);
179 }
180
181 return (ucp);
182 }
183
184 void
ucontext_free(ucontext_t * ucp)185 ucontext_free(ucontext_t *ucp)
186 {
187 free(ucp);
188 }
189