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Diffstat (limited to 'util/coroutine-sigaltstack.c')
| -rw-r--r-- | util/coroutine-sigaltstack.c | 293 |
1 files changed, 293 insertions, 0 deletions
diff --git a/util/coroutine-sigaltstack.c b/util/coroutine-sigaltstack.c new file mode 100644 index 0000000000..39842a4a90 --- /dev/null +++ b/util/coroutine-sigaltstack.c @@ -0,0 +1,293 @@ +/* + * sigaltstack coroutine initialization code + * + * Copyright (C) 2006 Anthony Liguori <anthony@codemonkey.ws> + * Copyright (C) 2011 Kevin Wolf <kwolf@redhat.com> + * Copyright (C) 2012 Alex Barcelo <abarcelo@ac.upc.edu> +** This file is partly based on pth_mctx.c, from the GNU Portable Threads +** Copyright (c) 1999-2006 Ralf S. Engelschall <rse@engelschall.com> + * + * This library is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; either + * version 2.1 of the License, or (at your option) any later version. + * + * This library is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with this library; if not, see <http://www.gnu.org/licenses/>. + */ + +/* XXX Is there a nicer way to disable glibc's stack check for longjmp? */ +#ifdef _FORTIFY_SOURCE +#undef _FORTIFY_SOURCE +#endif +#include <stdlib.h> +#include <setjmp.h> +#include <stdint.h> +#include <pthread.h> +#include <signal.h> +#include "qemu-common.h" +#include "qemu/coroutine_int.h" + +typedef struct { + Coroutine base; + void *stack; + sigjmp_buf env; +} CoroutineUContext; + +/** + * Per-thread coroutine bookkeeping + */ +typedef struct { + /** Currently executing coroutine */ + Coroutine *current; + + /** The default coroutine */ + CoroutineUContext leader; + + /** Information for the signal handler (trampoline) */ + sigjmp_buf tr_reenter; + volatile sig_atomic_t tr_called; + void *tr_handler; +} CoroutineThreadState; + +static pthread_key_t thread_state_key; + +static CoroutineThreadState *coroutine_get_thread_state(void) +{ + CoroutineThreadState *s = pthread_getspecific(thread_state_key); + + if (!s) { + s = g_malloc0(sizeof(*s)); + s->current = &s->leader.base; + pthread_setspecific(thread_state_key, s); + } + return s; +} + +static void qemu_coroutine_thread_cleanup(void *opaque) +{ + CoroutineThreadState *s = opaque; + + g_free(s); +} + +static void __attribute__((constructor)) coroutine_init(void) +{ + int ret; + + ret = pthread_key_create(&thread_state_key, qemu_coroutine_thread_cleanup); + if (ret != 0) { + fprintf(stderr, "unable to create leader key: %s\n", strerror(errno)); + abort(); + } +} + +/* "boot" function + * This is what starts the coroutine, is called from the trampoline + * (from the signal handler when it is not signal handling, read ahead + * for more information). + */ +static void coroutine_bootstrap(CoroutineUContext *self, Coroutine *co) +{ + /* Initialize longjmp environment and switch back the caller */ + if (!sigsetjmp(self->env, 0)) { + siglongjmp(*(sigjmp_buf *)co->entry_arg, 1); + } + + while (true) { + co->entry(co->entry_arg); + qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE); + } +} + +/* + * This is used as the signal handler. This is called with the brand new stack + * (thanks to sigaltstack). We have to return, given that this is a signal + * handler and the sigmask and some other things are changed. + */ +static void coroutine_trampoline(int signal) +{ + CoroutineUContext *self; + Coroutine *co; + CoroutineThreadState *coTS; + + /* Get the thread specific information */ + coTS = coroutine_get_thread_state(); + self = coTS->tr_handler; + coTS->tr_called = 1; + co = &self->base; + + /* + * Here we have to do a bit of a ping pong between the caller, given that + * this is a signal handler and we have to do a return "soon". Then the + * caller can reestablish everything and do a siglongjmp here again. + */ + if (!sigsetjmp(coTS->tr_reenter, 0)) { + return; + } + + /* + * Ok, the caller has siglongjmp'ed back to us, so now prepare + * us for the real machine state switching. We have to jump + * into another function here to get a new stack context for + * the auto variables (which have to be auto-variables + * because the start of the thread happens later). Else with + * PIC (i.e. Position Independent Code which is used when PTH + * is built as a shared library) most platforms would + * horrible core dump as experience showed. + */ + coroutine_bootstrap(self, co); +} + +Coroutine *qemu_coroutine_new(void) +{ + const size_t stack_size = 1 << 20; + CoroutineUContext *co; + CoroutineThreadState *coTS; + struct sigaction sa; + struct sigaction osa; + stack_t ss; + stack_t oss; + sigset_t sigs; + sigset_t osigs; + sigjmp_buf old_env; + + /* The way to manipulate stack is with the sigaltstack function. We + * prepare a stack, with it delivering a signal to ourselves and then + * put sigsetjmp/siglongjmp where needed. + * This has been done keeping coroutine-ucontext as a model and with the + * pth ideas (GNU Portable Threads). See coroutine-ucontext for the basics + * of the coroutines and see pth_mctx.c (from the pth project) for the + * sigaltstack way of manipulating stacks. + */ + + co = g_malloc0(sizeof(*co)); + co->stack = g_malloc(stack_size); + co->base.entry_arg = &old_env; /* stash away our jmp_buf */ + + coTS = coroutine_get_thread_state(); + coTS->tr_handler = co; + + /* + * Preserve the SIGUSR2 signal state, block SIGUSR2, + * and establish our signal handler. The signal will + * later transfer control onto the signal stack. + */ + sigemptyset(&sigs); + sigaddset(&sigs, SIGUSR2); + pthread_sigmask(SIG_BLOCK, &sigs, &osigs); + sa.sa_handler = coroutine_trampoline; + sigfillset(&sa.sa_mask); + sa.sa_flags = SA_ONSTACK; + if (sigaction(SIGUSR2, &sa, &osa) != 0) { + abort(); + } + + /* + * Set the new stack. + */ + ss.ss_sp = co->stack; + ss.ss_size = stack_size; + ss.ss_flags = 0; + if (sigaltstack(&ss, &oss) < 0) { + abort(); + } + + /* + * Now transfer control onto the signal stack and set it up. + * It will return immediately via "return" after the sigsetjmp() + * was performed. Be careful here with race conditions. The + * signal can be delivered the first time sigsuspend() is + * called. + */ + coTS->tr_called = 0; + pthread_kill(pthread_self(), SIGUSR2); + sigfillset(&sigs); + sigdelset(&sigs, SIGUSR2); + while (!coTS->tr_called) { + sigsuspend(&sigs); + } + + /* + * Inform the system that we are back off the signal stack by + * removing the alternative signal stack. Be careful here: It + * first has to be disabled, before it can be removed. + */ + sigaltstack(NULL, &ss); + ss.ss_flags = SS_DISABLE; + if (sigaltstack(&ss, NULL) < 0) { + abort(); + } + sigaltstack(NULL, &ss); + if (!(oss.ss_flags & SS_DISABLE)) { + sigaltstack(&oss, NULL); + } + + /* + * Restore the old SIGUSR2 signal handler and mask + */ + sigaction(SIGUSR2, &osa, NULL); + pthread_sigmask(SIG_SETMASK, &osigs, NULL); + + /* + * Now enter the trampoline again, but this time not as a signal + * handler. Instead we jump into it directly. The functionally + * redundant ping-pong pointer arithmetic is necessary to avoid + * type-conversion warnings related to the `volatile' qualifier and + * the fact that `jmp_buf' usually is an array type. + */ + if (!sigsetjmp(old_env, 0)) { + siglongjmp(coTS->tr_reenter, 1); + } + + /* + * Ok, we returned again, so now we're finished + */ + + return &co->base; +} + +void qemu_coroutine_delete(Coroutine *co_) +{ + CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_); + + g_free(co->stack); + g_free(co); +} + +CoroutineAction qemu_coroutine_switch(Coroutine *from_, Coroutine *to_, + CoroutineAction action) +{ + CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_); + CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_); + CoroutineThreadState *s = coroutine_get_thread_state(); + int ret; + + s->current = to_; + + ret = sigsetjmp(from->env, 0); + if (ret == 0) { + siglongjmp(to->env, action); + } + return ret; +} + +Coroutine *qemu_coroutine_self(void) +{ + CoroutineThreadState *s = coroutine_get_thread_state(); + + return s->current; +} + +bool qemu_in_coroutine(void) +{ + CoroutineThreadState *s = pthread_getspecific(thread_state_key); + + return s && s->current->caller; +} + |