/*
* 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"
#ifdef CONFIG_SAFESTACK
#error "SafeStack is not compatible with code run in alternate signal stacks"
#endif
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;
static pthread_mutex_t sigusr2_mutex = PTHREAD_MUTEX_INITIALIZER;
/* 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;
/*
* sigaction() is a process-global operation. We must not run
* this code in multiple threads at once.
*/
pthread_mutex_lock(&sigusr2_mutex);
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_mutex_unlock(&sigusr2_mutex);
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;
}
