blob: 2bb7e10d4bfcdfcaed47548b3909daf2ec475594 [file] [log] [blame]
* ucontext coroutine initialization code
* Copyright (C) 2006 Anthony Liguori <>
* Copyright (C) 2011 Kevin Wolf <>
* 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 2.0 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
* 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 <>.
/* XXX Is there a nicer way to disable glibc's stack check for longjmp? */
#include "qemu/osdep.h"
#include <ucontext.h>
#include "qemu-common.h"
#include "qemu/coroutine_int.h"
#include <valgrind/valgrind.h>
typedef struct {
Coroutine base;
void *stack;
sigjmp_buf env;
unsigned int valgrind_stack_id;
} CoroutineUContext;
* Per-thread coroutine bookkeeping
static __thread CoroutineUContext leader;
static __thread Coroutine *current;
* va_args to makecontext() must be type 'int', so passing
* the pointer we need may require several int args. This
* union is a quick hack to let us do that
union cc_arg {
void *p;
int i[2];
static void coroutine_trampoline(int i0, int i1)
union cc_arg arg;
CoroutineUContext *self;
Coroutine *co;
arg.i[0] = i0;
arg.i[1] = i1;
self = arg.p;
co = &self->base;
/* Initialize longjmp environment and switch back the caller */
if (!sigsetjmp(self->env, 0)) {
siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
while (true) {
qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
Coroutine *qemu_coroutine_new(void)
const size_t stack_size = 1 << 20;
CoroutineUContext *co;
ucontext_t old_uc, uc;
sigjmp_buf old_env;
union cc_arg arg = {0};
/* The ucontext functions preserve signal masks which incurs a
* system call overhead. sigsetjmp(buf, 0)/siglongjmp() does not
* preserve signal masks but only works on the current stack.
* Since we need a way to create and switch to a new stack, use
* the ucontext functions for that but sigsetjmp()/siglongjmp() for
* everything else.
if (getcontext(&uc) == -1) {
co = g_malloc0(sizeof(*co));
co->stack = g_malloc(stack_size);
co->base.entry_arg = &old_env; /* stash away our jmp_buf */
uc.uc_link = &old_uc;
uc.uc_stack.ss_sp = co->stack;
uc.uc_stack.ss_size = stack_size;
uc.uc_stack.ss_flags = 0;
co->valgrind_stack_id =
VALGRIND_STACK_REGISTER(co->stack, co->stack + stack_size);
arg.p = co;
makecontext(&uc, (void (*)(void))coroutine_trampoline,
2, arg.i[0], arg.i[1]);
/* swapcontext() in, siglongjmp() back out */
if (!sigsetjmp(old_env, 0)) {
swapcontext(&old_uc, &uc);
return &co->base;
/* Work around an unused variable in the valgrind.h macro... */
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-but-set-variable"
static inline void valgrind_stack_deregister(CoroutineUContext *co)
#pragma GCC diagnostic pop
void qemu_coroutine_delete(Coroutine *co_)
CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);
/* This function is marked noinline to prevent GCC from inlining it
* into coroutine_trampoline(). If we allow it to do that then it
* hoists the code to get the address of the TLS variable "current"
* out of the while() loop. This is an invalid transformation because
* the sigsetjmp() call may be called when running thread A but
* return in thread B, and so we might be in a different thread
* context each time round the loop.
CoroutineAction __attribute__((noinline))
qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
CoroutineAction action)
CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);
CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);
int ret;
current = to_;
ret = sigsetjmp(from->env, 0);
if (ret == 0) {
siglongjmp(to->env, action);
return ret;
Coroutine *qemu_coroutine_self(void)
if (!current) {
current = &leader.base;
return current;
bool qemu_in_coroutine(void)
return current && current->caller;