mirror of
https://gitlab.com/qemu-project/qemu
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194 lines
5.1 KiB
C
194 lines
5.1 KiB
C
/*
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* ucontext coroutine initialization code
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*
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* Copyright (C) 2006 Anthony Liguori <anthony@codemonkey.ws>
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* Copyright (C) 2011 Kevin Wolf <kwolf@redhat.com>
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.0 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, see <http://www.gnu.org/licenses/>.
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*/
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/* XXX Is there a nicer way to disable glibc's stack check for longjmp? */
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#ifdef _FORTIFY_SOURCE
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#undef _FORTIFY_SOURCE
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#endif
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#include "qemu/osdep.h"
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#include <ucontext.h>
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#include "qemu-common.h"
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#include "qemu/coroutine_int.h"
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#ifdef CONFIG_VALGRIND_H
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#include <valgrind/valgrind.h>
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#endif
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typedef struct {
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Coroutine base;
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void *stack;
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size_t stack_size;
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sigjmp_buf env;
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#ifdef CONFIG_VALGRIND_H
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unsigned int valgrind_stack_id;
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#endif
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} CoroutineUContext;
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/**
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* Per-thread coroutine bookkeeping
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*/
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static __thread CoroutineUContext leader;
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static __thread Coroutine *current;
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/*
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* va_args to makecontext() must be type 'int', so passing
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* the pointer we need may require several int args. This
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* union is a quick hack to let us do that
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*/
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union cc_arg {
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void *p;
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int i[2];
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};
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static void coroutine_trampoline(int i0, int i1)
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{
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union cc_arg arg;
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CoroutineUContext *self;
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Coroutine *co;
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arg.i[0] = i0;
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arg.i[1] = i1;
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self = arg.p;
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co = &self->base;
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/* Initialize longjmp environment and switch back the caller */
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if (!sigsetjmp(self->env, 0)) {
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siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
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}
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while (true) {
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co->entry(co->entry_arg);
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qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
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}
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}
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Coroutine *qemu_coroutine_new(void)
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{
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CoroutineUContext *co;
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ucontext_t old_uc, uc;
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sigjmp_buf old_env;
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union cc_arg arg = {0};
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/* The ucontext functions preserve signal masks which incurs a
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* system call overhead. sigsetjmp(buf, 0)/siglongjmp() does not
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* preserve signal masks but only works on the current stack.
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* Since we need a way to create and switch to a new stack, use
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* the ucontext functions for that but sigsetjmp()/siglongjmp() for
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* everything else.
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*/
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if (getcontext(&uc) == -1) {
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abort();
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}
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co = g_malloc0(sizeof(*co));
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co->stack_size = COROUTINE_STACK_SIZE;
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co->stack = qemu_alloc_stack(&co->stack_size);
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co->base.entry_arg = &old_env; /* stash away our jmp_buf */
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uc.uc_link = &old_uc;
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uc.uc_stack.ss_sp = co->stack;
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uc.uc_stack.ss_size = co->stack_size;
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uc.uc_stack.ss_flags = 0;
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#ifdef CONFIG_VALGRIND_H
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co->valgrind_stack_id =
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VALGRIND_STACK_REGISTER(co->stack, co->stack + co->stack_size);
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#endif
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arg.p = co;
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makecontext(&uc, (void (*)(void))coroutine_trampoline,
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2, arg.i[0], arg.i[1]);
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/* swapcontext() in, siglongjmp() back out */
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if (!sigsetjmp(old_env, 0)) {
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swapcontext(&old_uc, &uc);
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}
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return &co->base;
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}
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#ifdef CONFIG_VALGRIND_H
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#ifdef CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE
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/* Work around an unused variable in the valgrind.h macro... */
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#pragma GCC diagnostic push
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#pragma GCC diagnostic ignored "-Wunused-but-set-variable"
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#endif
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static inline void valgrind_stack_deregister(CoroutineUContext *co)
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{
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VALGRIND_STACK_DEREGISTER(co->valgrind_stack_id);
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}
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#ifdef CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE
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#pragma GCC diagnostic pop
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#endif
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#endif
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void qemu_coroutine_delete(Coroutine *co_)
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{
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CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);
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#ifdef CONFIG_VALGRIND_H
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valgrind_stack_deregister(co);
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#endif
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qemu_free_stack(co->stack, co->stack_size);
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g_free(co);
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}
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/* This function is marked noinline to prevent GCC from inlining it
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* into coroutine_trampoline(). If we allow it to do that then it
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* hoists the code to get the address of the TLS variable "current"
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* out of the while() loop. This is an invalid transformation because
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* the sigsetjmp() call may be called when running thread A but
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* return in thread B, and so we might be in a different thread
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* context each time round the loop.
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*/
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CoroutineAction __attribute__((noinline))
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qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
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CoroutineAction action)
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{
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CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);
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CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);
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int ret;
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current = to_;
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ret = sigsetjmp(from->env, 0);
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if (ret == 0) {
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siglongjmp(to->env, action);
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}
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return ret;
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}
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Coroutine *qemu_coroutine_self(void)
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{
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if (!current) {
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current = &leader.base;
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}
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return current;
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}
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bool qemu_in_coroutine(void)
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{
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return current && current->caller;
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}
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