/* * 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 "qemu/osdep.h" #include <pthread.h> #include "qemu-common.h" #include "qemu/coroutine_int.h" typedef struct { Coroutine base; void *stack; size_t stack_size; sigjmp_buf env; } CoroutineSigAltStack; /** * Per-thread coroutine bookkeeping */ typedef struct { /** Currently executing coroutine */ Coroutine *current; /** The default coroutine */ CoroutineSigAltStack 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(CoroutineSigAltStack *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) { CoroutineSigAltStack *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) { CoroutineSigAltStack *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_size = COROUTINE_STACK_SIZE; co->stack = qemu_alloc_stack(&co->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 = co->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_) { CoroutineSigAltStack *co = DO_UPCAST(CoroutineSigAltStack, base, co_); qemu_free_stack(co->stack, co->stack_size); g_free(co); } CoroutineAction qemu_coroutine_switch(Coroutine *from_, Coroutine *to_, CoroutineAction action) { CoroutineSigAltStack *from = DO_UPCAST(CoroutineSigAltStack, base, from_); CoroutineSigAltStack *to = DO_UPCAST(CoroutineSigAltStack, 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; }