Merge remote-tracking branch 'remotes/rth/tags/pull-tcg-20210921' into staging
[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 #ifdef CONFIG_SAFESTACK
34 #error "SafeStack is not compatible with code run in alternate signal stacks"
35 #endif
36
37 typedef struct {
38 Coroutine base;
39 void *stack;
40 size_t stack_size;
41 sigjmp_buf env;
42 } CoroutineSigAltStack;
43
44 /**
45 * Per-thread coroutine bookkeeping
46 */
47 typedef struct {
48 /** Currently executing coroutine */
49 Coroutine *current;
50
51 /** The default coroutine */
52 CoroutineSigAltStack leader;
53
54 /** Information for the signal handler (trampoline) */
55 sigjmp_buf tr_reenter;
56 volatile sig_atomic_t tr_called;
57 void *tr_handler;
58 } CoroutineThreadState;
59
60 static pthread_key_t thread_state_key;
61
62 static CoroutineThreadState *coroutine_get_thread_state(void)
63 {
64 CoroutineThreadState *s = pthread_getspecific(thread_state_key);
65
66 if (!s) {
67 s = g_malloc0(sizeof(*s));
68 s->current = &s->leader.base;
69 pthread_setspecific(thread_state_key, s);
70 }
71 return s;
72 }
73
74 static void qemu_coroutine_thread_cleanup(void *opaque)
75 {
76 CoroutineThreadState *s = opaque;
77
78 g_free(s);
79 }
80
81 static void __attribute__((constructor)) coroutine_init(void)
82 {
83 int ret;
84
85 ret = pthread_key_create(&thread_state_key, qemu_coroutine_thread_cleanup);
86 if (ret != 0) {
87 fprintf(stderr, "unable to create leader key: %s\n", strerror(errno));
88 abort();
89 }
90 }
91
92 /* "boot" function
93 * This is what starts the coroutine, is called from the trampoline
94 * (from the signal handler when it is not signal handling, read ahead
95 * for more information).
96 */
97 static void coroutine_bootstrap(CoroutineSigAltStack *self, Coroutine *co)
98 {
99 /* Initialize longjmp environment and switch back the caller */
100 if (!sigsetjmp(self->env, 0)) {
101 siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
102 }
103
104 while (true) {
105 co->entry(co->entry_arg);
106 qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
107 }
108 }
109
110 /*
111 * This is used as the signal handler. This is called with the brand new stack
112 * (thanks to sigaltstack). We have to return, given that this is a signal
113 * handler and the sigmask and some other things are changed.
114 */
115 static void coroutine_trampoline(int signal)
116 {
117 CoroutineSigAltStack *self;
118 Coroutine *co;
119 CoroutineThreadState *coTS;
120
121 /* Get the thread specific information */
122 coTS = coroutine_get_thread_state();
123 self = coTS->tr_handler;
124 coTS->tr_called = 1;
125 co = &self->base;
126
127 /*
128 * Here we have to do a bit of a ping pong between the caller, given that
129 * this is a signal handler and we have to do a return "soon". Then the
130 * caller can reestablish everything and do a siglongjmp here again.
131 */
132 if (!sigsetjmp(coTS->tr_reenter, 0)) {
133 return;
134 }
135
136 /*
137 * Ok, the caller has siglongjmp'ed back to us, so now prepare
138 * us for the real machine state switching. We have to jump
139 * into another function here to get a new stack context for
140 * the auto variables (which have to be auto-variables
141 * because the start of the thread happens later). Else with
142 * PIC (i.e. Position Independent Code which is used when PTH
143 * is built as a shared library) most platforms would
144 * horrible core dump as experience showed.
145 */
146 coroutine_bootstrap(self, co);
147 }
148
149 Coroutine *qemu_coroutine_new(void)
150 {
151 CoroutineSigAltStack *co;
152 CoroutineThreadState *coTS;
153 struct sigaction sa;
154 struct sigaction osa;
155 stack_t ss;
156 stack_t oss;
157 sigset_t sigs;
158 sigset_t osigs;
159 sigjmp_buf old_env;
160 static pthread_mutex_t sigusr2_mutex = PTHREAD_MUTEX_INITIALIZER;
161
162 /* The way to manipulate stack is with the sigaltstack function. We
163 * prepare a stack, with it delivering a signal to ourselves and then
164 * put sigsetjmp/siglongjmp where needed.
165 * This has been done keeping coroutine-ucontext as a model and with the
166 * pth ideas (GNU Portable Threads). See coroutine-ucontext for the basics
167 * of the coroutines and see pth_mctx.c (from the pth project) for the
168 * sigaltstack way of manipulating stacks.
169 */
170
171 co = g_malloc0(sizeof(*co));
172 co->stack_size = COROUTINE_STACK_SIZE;
173 co->stack = qemu_alloc_stack(&co->stack_size);
174 co->base.entry_arg = &old_env; /* stash away our jmp_buf */
175
176 coTS = coroutine_get_thread_state();
177 coTS->tr_handler = co;
178
179 /*
180 * Preserve the SIGUSR2 signal state, block SIGUSR2,
181 * and establish our signal handler. The signal will
182 * later transfer control onto the signal stack.
183 */
184 sigemptyset(&sigs);
185 sigaddset(&sigs, SIGUSR2);
186 pthread_sigmask(SIG_BLOCK, &sigs, &osigs);
187 sa.sa_handler = coroutine_trampoline;
188 sigfillset(&sa.sa_mask);
189 sa.sa_flags = SA_ONSTACK;
190
191 /*
192 * sigaction() is a process-global operation. We must not run
193 * this code in multiple threads at once.
194 */
195 pthread_mutex_lock(&sigusr2_mutex);
196 if (sigaction(SIGUSR2, &sa, &osa) != 0) {
197 abort();
198 }
199
200 /*
201 * Set the new stack.
202 */
203 ss.ss_sp = co->stack;
204 ss.ss_size = co->stack_size;
205 ss.ss_flags = 0;
206 if (sigaltstack(&ss, &oss) < 0) {
207 abort();
208 }
209
210 /*
211 * Now transfer control onto the signal stack and set it up.
212 * It will return immediately via "return" after the sigsetjmp()
213 * was performed. Be careful here with race conditions. The
214 * signal can be delivered the first time sigsuspend() is
215 * called.
216 */
217 coTS->tr_called = 0;
218 pthread_kill(pthread_self(), SIGUSR2);
219 sigfillset(&sigs);
220 sigdelset(&sigs, SIGUSR2);
221 while (!coTS->tr_called) {
222 sigsuspend(&sigs);
223 }
224
225 /*
226 * Inform the system that we are back off the signal stack by
227 * removing the alternative signal stack. Be careful here: It
228 * first has to be disabled, before it can be removed.
229 */
230 sigaltstack(NULL, &ss);
231 ss.ss_flags = SS_DISABLE;
232 if (sigaltstack(&ss, NULL) < 0) {
233 abort();
234 }
235 sigaltstack(NULL, &ss);
236 if (!(oss.ss_flags & SS_DISABLE)) {
237 sigaltstack(&oss, NULL);
238 }
239
240 /*
241 * Restore the old SIGUSR2 signal handler and mask
242 */
243 sigaction(SIGUSR2, &osa, NULL);
244 pthread_mutex_unlock(&sigusr2_mutex);
245
246 pthread_sigmask(SIG_SETMASK, &osigs, NULL);
247
248 /*
249 * Now enter the trampoline again, but this time not as a signal
250 * handler. Instead we jump into it directly. The functionally
251 * redundant ping-pong pointer arithmetic is necessary to avoid
252 * type-conversion warnings related to the `volatile' qualifier and
253 * the fact that `jmp_buf' usually is an array type.
254 */
255 if (!sigsetjmp(old_env, 0)) {
256 siglongjmp(coTS->tr_reenter, 1);
257 }
258
259 /*
260 * Ok, we returned again, so now we're finished
261 */
262
263 return &co->base;
264 }
265
266 void qemu_coroutine_delete(Coroutine *co_)
267 {
268 CoroutineSigAltStack *co = DO_UPCAST(CoroutineSigAltStack, base, co_);
269
270 qemu_free_stack(co->stack, co->stack_size);
271 g_free(co);
272 }
273
274 CoroutineAction qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
275 CoroutineAction action)
276 {
277 CoroutineSigAltStack *from = DO_UPCAST(CoroutineSigAltStack, base, from_);
278 CoroutineSigAltStack *to = DO_UPCAST(CoroutineSigAltStack, base, to_);
279 CoroutineThreadState *s = coroutine_get_thread_state();
280 int ret;
281
282 s->current = to_;
283
284 ret = sigsetjmp(from->env, 0);
285 if (ret == 0) {
286 siglongjmp(to->env, action);
287 }
288 return ret;
289 }
290
291 Coroutine *qemu_coroutine_self(void)
292 {
293 CoroutineThreadState *s = coroutine_get_thread_state();
294
295 return s->current;
296 }
297
298 bool qemu_in_coroutine(void)
299 {
300 CoroutineThreadState *s = pthread_getspecific(thread_state_key);
301
302 return s && s->current->caller;
303 }
304