Merge tag 'edgar/xilinx-next-2022-09-21.for-upstream' of https://github.com/edgarigl...
[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/coroutine_int.h"
31
32 #ifdef CONFIG_SAFESTACK
33 #error "SafeStack is not compatible with code run in alternate signal stacks"
34 #endif
35
36 typedef struct {
37 Coroutine base;
38 void *stack;
39 size_t stack_size;
40 sigjmp_buf env;
41 } CoroutineSigAltStack;
42
43 /**
44 * Per-thread coroutine bookkeeping
45 */
46 typedef struct {
47 /** Currently executing coroutine */
48 Coroutine *current;
49
50 /** The default coroutine */
51 CoroutineSigAltStack leader;
52
53 /** Information for the signal handler (trampoline) */
54 sigjmp_buf tr_reenter;
55 volatile sig_atomic_t tr_called;
56 void *tr_handler;
57 } CoroutineThreadState;
58
59 static pthread_key_t thread_state_key;
60
61 static CoroutineThreadState *coroutine_get_thread_state(void)
62 {
63 CoroutineThreadState *s = pthread_getspecific(thread_state_key);
64
65 if (!s) {
66 s = g_malloc0(sizeof(*s));
67 s->current = &s->leader.base;
68 pthread_setspecific(thread_state_key, s);
69 }
70 return s;
71 }
72
73 static void qemu_coroutine_thread_cleanup(void *opaque)
74 {
75 CoroutineThreadState *s = opaque;
76
77 g_free(s);
78 }
79
80 static void __attribute__((constructor)) coroutine_init(void)
81 {
82 int ret;
83
84 ret = pthread_key_create(&thread_state_key, qemu_coroutine_thread_cleanup);
85 if (ret != 0) {
86 fprintf(stderr, "unable to create leader key: %s\n", strerror(errno));
87 abort();
88 }
89 }
90
91 /* "boot" function
92 * This is what starts the coroutine, is called from the trampoline
93 * (from the signal handler when it is not signal handling, read ahead
94 * for more information).
95 */
96 static void coroutine_bootstrap(CoroutineSigAltStack *self, Coroutine *co)
97 {
98 /* Initialize longjmp environment and switch back the caller */
99 if (!sigsetjmp(self->env, 0)) {
100 siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
101 }
102
103 while (true) {
104 co->entry(co->entry_arg);
105 qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
106 }
107 }
108
109 /*
110 * This is used as the signal handler. This is called with the brand new stack
111 * (thanks to sigaltstack). We have to return, given that this is a signal
112 * handler and the sigmask and some other things are changed.
113 */
114 static void coroutine_trampoline(int signal)
115 {
116 CoroutineSigAltStack *self;
117 Coroutine *co;
118 CoroutineThreadState *coTS;
119
120 /* Get the thread specific information */
121 coTS = coroutine_get_thread_state();
122 self = coTS->tr_handler;
123 coTS->tr_called = 1;
124 co = &self->base;
125
126 /*
127 * Here we have to do a bit of a ping pong between the caller, given that
128 * this is a signal handler and we have to do a return "soon". Then the
129 * caller can reestablish everything and do a siglongjmp here again.
130 */
131 if (!sigsetjmp(coTS->tr_reenter, 0)) {
132 return;
133 }
134
135 /*
136 * Ok, the caller has siglongjmp'ed back to us, so now prepare
137 * us for the real machine state switching. We have to jump
138 * into another function here to get a new stack context for
139 * the auto variables (which have to be auto-variables
140 * because the start of the thread happens later). Else with
141 * PIC (i.e. Position Independent Code which is used when PTH
142 * is built as a shared library) most platforms would
143 * horrible core dump as experience showed.
144 */
145 coroutine_bootstrap(self, co);
146 }
147
148 Coroutine *qemu_coroutine_new(void)
149 {
150 CoroutineSigAltStack *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 sigjmp_buf old_env;
159 static pthread_mutex_t sigusr2_mutex = PTHREAD_MUTEX_INITIALIZER;
160
161 /* The way to manipulate stack is with the sigaltstack function. We
162 * prepare a stack, with it delivering a signal to ourselves and then
163 * put sigsetjmp/siglongjmp where needed.
164 * This has been done keeping coroutine-ucontext as a model and with the
165 * pth ideas (GNU Portable Threads). See coroutine-ucontext for the basics
166 * of the coroutines and see pth_mctx.c (from the pth project) for the
167 * sigaltstack way of manipulating stacks.
168 */
169
170 co = g_malloc0(sizeof(*co));
171 co->stack_size = COROUTINE_STACK_SIZE;
172 co->stack = qemu_alloc_stack(&co->stack_size);
173 co->base.entry_arg = &old_env; /* stash away our jmp_buf */
174
175 coTS = coroutine_get_thread_state();
176 coTS->tr_handler = co;
177
178 /*
179 * Preserve the SIGUSR2 signal state, block SIGUSR2,
180 * and establish our signal handler. The signal will
181 * later transfer control onto the signal stack.
182 */
183 sigemptyset(&sigs);
184 sigaddset(&sigs, SIGUSR2);
185 pthread_sigmask(SIG_BLOCK, &sigs, &osigs);
186 sa.sa_handler = coroutine_trampoline;
187 sigfillset(&sa.sa_mask);
188 sa.sa_flags = SA_ONSTACK;
189
190 /*
191 * sigaction() is a process-global operation. We must not run
192 * this code in multiple threads at once.
193 */
194 pthread_mutex_lock(&sigusr2_mutex);
195 if (sigaction(SIGUSR2, &sa, &osa) != 0) {
196 abort();
197 }
198
199 /*
200 * Set the new stack.
201 */
202 ss.ss_sp = co->stack;
203 ss.ss_size = co->stack_size;
204 ss.ss_flags = 0;
205 if (sigaltstack(&ss, &oss) < 0) {
206 abort();
207 }
208
209 /*
210 * Now transfer control onto the signal stack and set it up.
211 * It will return immediately via "return" after the sigsetjmp()
212 * was performed. Be careful here with race conditions. The
213 * signal can be delivered the first time sigsuspend() is
214 * called.
215 */
216 coTS->tr_called = 0;
217 pthread_kill(pthread_self(), SIGUSR2);
218 sigfillset(&sigs);
219 sigdelset(&sigs, SIGUSR2);
220 while (!coTS->tr_called) {
221 sigsuspend(&sigs);
222 }
223
224 /*
225 * Inform the system that we are back off the signal stack by
226 * removing the alternative signal stack. Be careful here: It
227 * first has to be disabled, before it can be removed.
228 */
229 sigaltstack(NULL, &ss);
230 ss.ss_flags = SS_DISABLE;
231 if (sigaltstack(&ss, NULL) < 0) {
232 abort();
233 }
234 sigaltstack(NULL, &ss);
235 if (!(oss.ss_flags & SS_DISABLE)) {
236 sigaltstack(&oss, NULL);
237 }
238
239 /*
240 * Restore the old SIGUSR2 signal handler and mask
241 */
242 sigaction(SIGUSR2, &osa, NULL);
243 pthread_mutex_unlock(&sigusr2_mutex);
244
245 pthread_sigmask(SIG_SETMASK, &osigs, NULL);
246
247 /*
248 * Now enter the trampoline again, but this time not as a signal
249 * handler. Instead we jump into it directly. The functionally
250 * redundant ping-pong pointer arithmetic is necessary to avoid
251 * type-conversion warnings related to the `volatile' qualifier and
252 * the fact that `jmp_buf' usually is an array type.
253 */
254 if (!sigsetjmp(old_env, 0)) {
255 siglongjmp(coTS->tr_reenter, 1);
256 }
257
258 /*
259 * Ok, we returned again, so now we're finished
260 */
261
262 return &co->base;
263 }
264
265 void qemu_coroutine_delete(Coroutine *co_)
266 {
267 CoroutineSigAltStack *co = DO_UPCAST(CoroutineSigAltStack, base, co_);
268
269 qemu_free_stack(co->stack, co->stack_size);
270 g_free(co);
271 }
272
273 CoroutineAction qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
274 CoroutineAction action)
275 {
276 CoroutineSigAltStack *from = DO_UPCAST(CoroutineSigAltStack, base, from_);
277 CoroutineSigAltStack *to = DO_UPCAST(CoroutineSigAltStack, base, to_);
278 CoroutineThreadState *s = coroutine_get_thread_state();
279 int ret;
280
281 s->current = to_;
282
283 ret = sigsetjmp(from->env, 0);
284 if (ret == 0) {
285 siglongjmp(to->env, action);
286 }
287 return ret;
288 }
289
290 Coroutine *qemu_coroutine_self(void)
291 {
292 CoroutineThreadState *s = coroutine_get_thread_state();
293
294 return s->current;
295 }
296
297 bool qemu_in_coroutine(void)
298 {
299 CoroutineThreadState *s = pthread_getspecific(thread_state_key);
300
301 return s && s->current->caller;
302 }
303