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Diffstat (limited to 'util/coroutine-ucontext.c')
| -rw-r--r-- | util/coroutine-ucontext.c | 194 |
1 files changed, 194 insertions, 0 deletions
diff --git a/util/coroutine-ucontext.c b/util/coroutine-ucontext.c new file mode 100644 index 0000000000..26cbebb7a7 --- /dev/null +++ b/util/coroutine-ucontext.c @@ -0,0 +1,194 @@ +/* + * ucontext coroutine initialization code + * + * Copyright (C) 2006 Anthony Liguori <anthony@codemonkey.ws> + * Copyright (C) 2011 Kevin Wolf <kwolf@redhat.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 2.0 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 + * 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 <ucontext.h> +#include "qemu-common.h" +#include "qemu/coroutine_int.h" + +#ifdef CONFIG_VALGRIND_H +#include <valgrind/valgrind.h> +#endif + +typedef struct { + Coroutine base; + void *stack; + sigjmp_buf env; + +#ifdef CONFIG_VALGRIND_H + unsigned int valgrind_stack_id; +#endif + +} 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) { + co->entry(co->entry_arg); + 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) { + abort(); + } + + 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; + +#ifdef CONFIG_VALGRIND_H + co->valgrind_stack_id = + VALGRIND_STACK_REGISTER(co->stack, co->stack + stack_size); +#endif + + 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; +} + +#ifdef CONFIG_VALGRIND_H +#ifdef CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE +/* Work around an unused variable in the valgrind.h macro... */ +#pragma GCC diagnostic push +#pragma GCC diagnostic ignored "-Wunused-but-set-variable" +#endif +static inline void valgrind_stack_deregister(CoroutineUContext *co) +{ + VALGRIND_STACK_DEREGISTER(co->valgrind_stack_id); +} +#ifdef CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE +#pragma GCC diagnostic pop +#endif +#endif + +void qemu_coroutine_delete(Coroutine *co_) +{ + CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_); + +#ifdef CONFIG_VALGRIND_H + valgrind_stack_deregister(co); +#endif + + g_free(co->stack); + g_free(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; +} |