target-xtensa: add entry overflow test
[qemu.git] / 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 <stdlib.h>
29 #include <setjmp.h>
30 #include <stdint.h>
31 #include <pthread.h>
32 #include <signal.h>
33 #include "qemu-common.h"
34 #include "block/coroutine_int.h"
35
36 typedef struct {
37 Coroutine base;
38 void *stack;
39 sigjmp_buf env;
40 } CoroutineUContext;
41
42 /**
43 * Per-thread coroutine bookkeeping
44 */
45 typedef struct {
46 /** Currently executing coroutine */
47 Coroutine *current;
48
49 /** The default coroutine */
50 CoroutineUContext leader;
51
52 /** Information for the signal handler (trampoline) */
53 sigjmp_buf tr_reenter;
54 volatile sig_atomic_t tr_called;
55 void *tr_handler;
56 } CoroutineThreadState;
57
58 static pthread_key_t thread_state_key;
59
60 static CoroutineThreadState *coroutine_get_thread_state(void)
61 {
62 CoroutineThreadState *s = pthread_getspecific(thread_state_key);
63
64 if (!s) {
65 s = g_malloc0(sizeof(*s));
66 s->current = &s->leader.base;
67 pthread_setspecific(thread_state_key, s);
68 }
69 return s;
70 }
71
72 static void qemu_coroutine_thread_cleanup(void *opaque)
73 {
74 CoroutineThreadState *s = opaque;
75
76 g_free(s);
77 }
78
79 static void __attribute__((constructor)) coroutine_init(void)
80 {
81 int ret;
82
83 ret = pthread_key_create(&thread_state_key, qemu_coroutine_thread_cleanup);
84 if (ret != 0) {
85 fprintf(stderr, "unable to create leader key: %s\n", strerror(errno));
86 abort();
87 }
88 }
89
90 /* "boot" function
91 * This is what starts the coroutine, is called from the trampoline
92 * (from the signal handler when it is not signal handling, read ahead
93 * for more information).
94 */
95 static void coroutine_bootstrap(CoroutineUContext *self, Coroutine *co)
96 {
97 /* Initialize longjmp environment and switch back the caller */
98 if (!sigsetjmp(self->env, 0)) {
99 siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
100 }
101
102 while (true) {
103 co->entry(co->entry_arg);
104 qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
105 }
106 }
107
108 /*
109 * This is used as the signal handler. This is called with the brand new stack
110 * (thanks to sigaltstack). We have to return, given that this is a signal
111 * handler and the sigmask and some other things are changed.
112 */
113 static void coroutine_trampoline(int signal)
114 {
115 CoroutineUContext *self;
116 Coroutine *co;
117 CoroutineThreadState *coTS;
118
119 /* Get the thread specific information */
120 coTS = coroutine_get_thread_state();
121 self = coTS->tr_handler;
122 coTS->tr_called = 1;
123 co = &self->base;
124
125 /*
126 * Here we have to do a bit of a ping pong between the caller, given that
127 * this is a signal handler and we have to do a return "soon". Then the
128 * caller can reestablish everything and do a siglongjmp here again.
129 */
130 if (!sigsetjmp(coTS->tr_reenter, 0)) {
131 return;
132 }
133
134 /*
135 * Ok, the caller has siglongjmp'ed back to us, so now prepare
136 * us for the real machine state switching. We have to jump
137 * into another function here to get a new stack context for
138 * the auto variables (which have to be auto-variables
139 * because the start of the thread happens later). Else with
140 * PIC (i.e. Position Independent Code which is used when PTH
141 * is built as a shared library) most platforms would
142 * horrible core dump as experience showed.
143 */
144 coroutine_bootstrap(self, co);
145 }
146
147 Coroutine *qemu_coroutine_new(void)
148 {
149 const size_t stack_size = 1 << 20;
150 CoroutineUContext *co;
151 CoroutineThreadState *coTS;
152 struct sigaction sa;
153 struct sigaction osa;
154 stack_t ss;
155 stack_t oss;
156 sigset_t sigs;
157 sigset_t osigs;
158 jmp_buf old_env;
159
160 /* The way to manipulate stack is with the sigaltstack function. We
161 * prepare a stack, with it delivering a signal to ourselves and then
162 * put sigsetjmp/siglongjmp where needed.
163 * This has been done keeping coroutine-ucontext as a model and with the
164 * pth ideas (GNU Portable Threads). See coroutine-ucontext for the basics
165 * of the coroutines and see pth_mctx.c (from the pth project) for the
166 * sigaltstack way of manipulating stacks.
167 */
168
169 co = g_malloc0(sizeof(*co));
170 co->stack = g_malloc(stack_size);
171 co->base.entry_arg = &old_env; /* stash away our jmp_buf */
172
173 coTS = coroutine_get_thread_state();
174 coTS->tr_handler = co;
175
176 /*
177 * Preserve the SIGUSR2 signal state, block SIGUSR2,
178 * and establish our signal handler. The signal will
179 * later transfer control onto the signal stack.
180 */
181 sigemptyset(&sigs);
182 sigaddset(&sigs, SIGUSR2);
183 pthread_sigmask(SIG_BLOCK, &sigs, &osigs);
184 sa.sa_handler = coroutine_trampoline;
185 sigfillset(&sa.sa_mask);
186 sa.sa_flags = SA_ONSTACK;
187 if (sigaction(SIGUSR2, &sa, &osa) != 0) {
188 abort();
189 }
190
191 /*
192 * Set the new stack.
193 */
194 ss.ss_sp = co->stack;
195 ss.ss_size = stack_size;
196 ss.ss_flags = 0;
197 if (sigaltstack(&ss, &oss) < 0) {
198 abort();
199 }
200
201 /*
202 * Now transfer control onto the signal stack and set it up.
203 * It will return immediately via "return" after the sigsetjmp()
204 * was performed. Be careful here with race conditions. The
205 * signal can be delivered the first time sigsuspend() is
206 * called.
207 */
208 coTS->tr_called = 0;
209 pthread_kill(pthread_self(), SIGUSR2);
210 sigfillset(&sigs);
211 sigdelset(&sigs, SIGUSR2);
212 while (!coTS->tr_called) {
213 sigsuspend(&sigs);
214 }
215
216 /*
217 * Inform the system that we are back off the signal stack by
218 * removing the alternative signal stack. Be careful here: It
219 * first has to be disabled, before it can be removed.
220 */
221 sigaltstack(NULL, &ss);
222 ss.ss_flags = SS_DISABLE;
223 if (sigaltstack(&ss, NULL) < 0) {
224 abort();
225 }
226 sigaltstack(NULL, &ss);
227 if (!(oss.ss_flags & SS_DISABLE)) {
228 sigaltstack(&oss, NULL);
229 }
230
231 /*
232 * Restore the old SIGUSR2 signal handler and mask
233 */
234 sigaction(SIGUSR2, &osa, NULL);
235 pthread_sigmask(SIG_SETMASK, &osigs, NULL);
236
237 /*
238 * Now enter the trampoline again, but this time not as a signal
239 * handler. Instead we jump into it directly. The functionally
240 * redundant ping-pong pointer arithmetic is necessary to avoid
241 * type-conversion warnings related to the `volatile' qualifier and
242 * the fact that `jmp_buf' usually is an array type.
243 */
244 if (!sigsetjmp(old_env, 0)) {
245 siglongjmp(coTS->tr_reenter, 1);
246 }
247
248 /*
249 * Ok, we returned again, so now we're finished
250 */
251
252 return &co->base;
253 }
254
255 void qemu_coroutine_delete(Coroutine *co_)
256 {
257 CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);
258
259 g_free(co->stack);
260 g_free(co);
261 }
262
263 CoroutineAction qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
264 CoroutineAction action)
265 {
266 CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);
267 CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);
268 CoroutineThreadState *s = coroutine_get_thread_state();
269 int ret;
270
271 s->current = to_;
272
273 ret = sigsetjmp(from->env, 0);
274 if (ret == 0) {
275 siglongjmp(to->env, action);
276 }
277 return ret;
278 }
279
280 Coroutine *qemu_coroutine_self(void)
281 {
282 CoroutineThreadState *s = coroutine_get_thread_state();
283
284 return s->current;
285 }
286
287 bool qemu_in_coroutine(void)
288 {
289 CoroutineThreadState *s = pthread_getspecific(thread_state_key);
290
291 return s && s->current->caller;
292 }
293