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[qemu.git] / util / coroutine-sigaltstack.c
1 /*
2 * sigaltstack coroutine initialization code
3 *
4 * Copyright (C) 2006 Anthony Liguori <anthony@codemonkey.ws>
5 * Copyright (C) 2011 Kevin Wolf <kwolf@redhat.com>
6 * Copyright (C) 2012 Alex Barcelo <abarcelo@ac.upc.edu>
7 ** This file is partly based on pth_mctx.c, from the GNU Portable Threads
8 ** Copyright (c) 1999-2006 Ralf S. Engelschall <rse@engelschall.com>
9 *
10 * This library is free software; you can redistribute it and/or
11 * modify it under the terms of the GNU Lesser General Public
12 * License as published by the Free Software Foundation; either
13 * version 2.1 of the License, or (at your option) any later version.
14 *
15 * This library is distributed in the hope that it will be useful,
16 * but WITHOUT ANY WARRANTY; without even the implied warranty of
17 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
18 * Lesser General Public License for more details.
19 *
20 * You should have received a copy of the GNU Lesser General Public
21 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
22 */
23
24 /* XXX Is there a nicer way to disable glibc's stack check for longjmp? */
25 #ifdef _FORTIFY_SOURCE
26 #undef _FORTIFY_SOURCE
27 #endif
28 #include "qemu/osdep.h"
29 #include <pthread.h>
30 #include "qemu-common.h"
31 #include "qemu/coroutine_int.h"
32
33 typedef struct {
34 Coroutine base;
35 void *stack;
36 size_t stack_size;
37 sigjmp_buf env;
38 } CoroutineSigAltStack;
39
40 /**
41 * Per-thread coroutine bookkeeping
42 */
43 typedef struct {
44 /** Currently executing coroutine */
45 Coroutine *current;
46
47 /** The default coroutine */
48 CoroutineSigAltStack leader;
49
50 /** Information for the signal handler (trampoline) */
51 sigjmp_buf tr_reenter;
52 volatile sig_atomic_t tr_called;
53 void *tr_handler;
54 } CoroutineThreadState;
55
56 static pthread_key_t thread_state_key;
57
58 static CoroutineThreadState *coroutine_get_thread_state(void)
59 {
60 CoroutineThreadState *s = pthread_getspecific(thread_state_key);
61
62 if (!s) {
63 s = g_malloc0(sizeof(*s));
64 s->current = &s->leader.base;
65 pthread_setspecific(thread_state_key, s);
66 }
67 return s;
68 }
69
70 static void qemu_coroutine_thread_cleanup(void *opaque)
71 {
72 CoroutineThreadState *s = opaque;
73
74 g_free(s);
75 }
76
77 static void __attribute__((constructor)) coroutine_init(void)
78 {
79 int ret;
80
81 ret = pthread_key_create(&thread_state_key, qemu_coroutine_thread_cleanup);
82 if (ret != 0) {
83 fprintf(stderr, "unable to create leader key: %s\n", strerror(errno));
84 abort();
85 }
86 }
87
88 /* "boot" function
89 * This is what starts the coroutine, is called from the trampoline
90 * (from the signal handler when it is not signal handling, read ahead
91 * for more information).
92 */
93 static void coroutine_bootstrap(CoroutineSigAltStack *self, Coroutine *co)
94 {
95 /* Initialize longjmp environment and switch back the caller */
96 if (!sigsetjmp(self->env, 0)) {
97 siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
98 }
99
100 while (true) {
101 co->entry(co->entry_arg);
102 qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
103 }
104 }
105
106 /*
107 * This is used as the signal handler. This is called with the brand new stack
108 * (thanks to sigaltstack). We have to return, given that this is a signal
109 * handler and the sigmask and some other things are changed.
110 */
111 static void coroutine_trampoline(int signal)
112 {
113 CoroutineSigAltStack *self;
114 Coroutine *co;
115 CoroutineThreadState *coTS;
116
117 /* Get the thread specific information */
118 coTS = coroutine_get_thread_state();
119 self = coTS->tr_handler;
120 coTS->tr_called = 1;
121 co = &self->base;
122
123 /*
124 * Here we have to do a bit of a ping pong between the caller, given that
125 * this is a signal handler and we have to do a return "soon". Then the
126 * caller can reestablish everything and do a siglongjmp here again.
127 */
128 if (!sigsetjmp(coTS->tr_reenter, 0)) {
129 return;
130 }
131
132 /*
133 * Ok, the caller has siglongjmp'ed back to us, so now prepare
134 * us for the real machine state switching. We have to jump
135 * into another function here to get a new stack context for
136 * the auto variables (which have to be auto-variables
137 * because the start of the thread happens later). Else with
138 * PIC (i.e. Position Independent Code which is used when PTH
139 * is built as a shared library) most platforms would
140 * horrible core dump as experience showed.
141 */
142 coroutine_bootstrap(self, co);
143 }
144
145 Coroutine *qemu_coroutine_new(void)
146 {
147 CoroutineSigAltStack *co;
148 CoroutineThreadState *coTS;
149 struct sigaction sa;
150 struct sigaction osa;
151 stack_t ss;
152 stack_t oss;
153 sigset_t sigs;
154 sigset_t osigs;
155 sigjmp_buf old_env;
156
157 /* The way to manipulate stack is with the sigaltstack function. We
158 * prepare a stack, with it delivering a signal to ourselves and then
159 * put sigsetjmp/siglongjmp where needed.
160 * This has been done keeping coroutine-ucontext as a model and with the
161 * pth ideas (GNU Portable Threads). See coroutine-ucontext for the basics
162 * of the coroutines and see pth_mctx.c (from the pth project) for the
163 * sigaltstack way of manipulating stacks.
164 */
165
166 co = g_malloc0(sizeof(*co));
167 co->stack_size = COROUTINE_STACK_SIZE;
168 co->stack = qemu_alloc_stack(&co->stack_size);
169 co->base.entry_arg = &old_env; /* stash away our jmp_buf */
170
171 coTS = coroutine_get_thread_state();
172 coTS->tr_handler = co;
173
174 /*
175 * Preserve the SIGUSR2 signal state, block SIGUSR2,
176 * and establish our signal handler. The signal will
177 * later transfer control onto the signal stack.
178 */
179 sigemptyset(&sigs);
180 sigaddset(&sigs, SIGUSR2);
181 pthread_sigmask(SIG_BLOCK, &sigs, &osigs);
182 sa.sa_handler = coroutine_trampoline;
183 sigfillset(&sa.sa_mask);
184 sa.sa_flags = SA_ONSTACK;
185 if (sigaction(SIGUSR2, &sa, &osa) != 0) {
186 abort();
187 }
188
189 /*
190 * Set the new stack.
191 */
192 ss.ss_sp = co->stack;
193 ss.ss_size = co->stack_size;
194 ss.ss_flags = 0;
195 if (sigaltstack(&ss, &oss) < 0) {
196 abort();
197 }
198
199 /*
200 * Now transfer control onto the signal stack and set it up.
201 * It will return immediately via "return" after the sigsetjmp()
202 * was performed. Be careful here with race conditions. The
203 * signal can be delivered the first time sigsuspend() is
204 * called.
205 */
206 coTS->tr_called = 0;
207 pthread_kill(pthread_self(), SIGUSR2);
208 sigfillset(&sigs);
209 sigdelset(&sigs, SIGUSR2);
210 while (!coTS->tr_called) {
211 sigsuspend(&sigs);
212 }
213
214 /*
215 * Inform the system that we are back off the signal stack by
216 * removing the alternative signal stack. Be careful here: It
217 * first has to be disabled, before it can be removed.
218 */
219 sigaltstack(NULL, &ss);
220 ss.ss_flags = SS_DISABLE;
221 if (sigaltstack(&ss, NULL) < 0) {
222 abort();
223 }
224 sigaltstack(NULL, &ss);
225 if (!(oss.ss_flags & SS_DISABLE)) {
226 sigaltstack(&oss, NULL);
227 }
228
229 /*
230 * Restore the old SIGUSR2 signal handler and mask
231 */
232 sigaction(SIGUSR2, &osa, NULL);
233 pthread_sigmask(SIG_SETMASK, &osigs, NULL);
234
235 /*
236 * Now enter the trampoline again, but this time not as a signal
237 * handler. Instead we jump into it directly. The functionally
238 * redundant ping-pong pointer arithmetic is necessary to avoid
239 * type-conversion warnings related to the `volatile' qualifier and
240 * the fact that `jmp_buf' usually is an array type.
241 */
242 if (!sigsetjmp(old_env, 0)) {
243 siglongjmp(coTS->tr_reenter, 1);
244 }
245
246 /*
247 * Ok, we returned again, so now we're finished
248 */
249
250 return &co->base;
251 }
252
253 void qemu_coroutine_delete(Coroutine *co_)
254 {
255 CoroutineSigAltStack *co = DO_UPCAST(CoroutineSigAltStack, base, co_);
256
257 qemu_free_stack(co->stack, co->stack_size);
258 g_free(co);
259 }
260
261 CoroutineAction qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
262 CoroutineAction action)
263 {
264 CoroutineSigAltStack *from = DO_UPCAST(CoroutineSigAltStack, base, from_);
265 CoroutineSigAltStack *to = DO_UPCAST(CoroutineSigAltStack, base, to_);
266 CoroutineThreadState *s = coroutine_get_thread_state();
267 int ret;
268
269 s->current = to_;
270
271 ret = sigsetjmp(from->env, 0);
272 if (ret == 0) {
273 siglongjmp(to->env, action);
274 }
275 return ret;
276 }
277
278 Coroutine *qemu_coroutine_self(void)
279 {
280 CoroutineThreadState *s = coroutine_get_thread_state();
281
282 return s->current;
283 }
284
285 bool qemu_in_coroutine(void)
286 {
287 CoroutineThreadState *s = pthread_getspecific(thread_state_key);
288
289 return s && s->current->caller;
290 }
291