text: /*
   * 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 "qemu/osdep.h"
  #include <ucontext.h>
  #include "qemu-common.h"
  #include "qemu/coroutine_int.h"
  
  #ifdef CONFIG_VALGRIND_H
  #include <valgrind/valgrind.h>
  #endif
  
  #if defined(__SANITIZE_ADDRESS__) || __has_feature(address_sanitizer)
  #ifdef CONFIG_ASAN_IFACE_FIBER
  #define CONFIG_ASAN 1
  #include <sanitizer/asan_interface.h>
  #endif
  #endif
  
  typedef struct {
      Coroutine base;
      void *stack;
      size_t stack_size;
      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 finish_switch_fiber(void *fake_stack_save)
  {
  #ifdef CONFIG_ASAN
      const void *bottom_old;
      size_t size_old;
  
      __sanitizer_finish_switch_fiber(fake_stack_save, &bottom_old, &size_old);
  
      if (!leader.stack) {
          leader.stack = (void *)bottom_old;
          leader.stack_size = size_old;
      }
  #endif
  }
  
  static void start_switch_fiber(void **fake_stack_save,
                                 const void *bottom, size_t size)
  {
  #ifdef CONFIG_ASAN
      __sanitizer_start_switch_fiber(fake_stack_save, bottom, size);
  #endif
  }
  
  static void coroutine_trampoline(int i0, int i1)
  {
      union cc_arg arg;
      CoroutineUContext *self;
      Coroutine *co;
      void *fake_stack_save = NULL;
  
      finish_switch_fiber(NULL);
  
      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)) {
          start_switch_fiber(&fake_stack_save,
                             leader.stack, leader.stack_size);
          siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
      }
  
      finish_switch_fiber(fake_stack_save);
  
      while (true) {
          co->entry(co->entry_arg);
          qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
      }
  }
  
  Coroutine *qemu_coroutine_new(void)
  {
      CoroutineUContext *co;
      ucontext_t old_uc, uc;
      sigjmp_buf old_env;
      union cc_arg arg = {0};
      void *fake_stack_save = NULL;
  
      /* 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_size = COROUTINE_STACK_SIZE;
      co->stack = qemu_alloc_stack(&co->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 = co->stack_size;
      uc.uc_stack.ss_flags = 0;
  
  #ifdef CONFIG_VALGRIND_H
      co->valgrind_stack_id =
          VALGRIND_STACK_REGISTER(co->stack, co->stack + co->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)) {
          start_switch_fiber(&fake_stack_save, co->stack, co->stack_size);
          swapcontext(&old_uc, &uc);
      }
  
      finish_switch_fiber(fake_stack_save);
  
      return &co->base;
  }
  
  #ifdef CONFIG_VALGRIND_H
  #if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && !defined(__clang__)
  /* 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);
  }
  #if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && !defined(__clang__)
  #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
  
      qemu_free_stack(co->stack, co->stack_size);
      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;
      void *fake_stack_save = NULL;
  
      current = to_;
  
      ret = sigsetjmp(from->env, 0);
      if (ret == 0) {
          start_switch_fiber(action == COROUTINE_TERMINATE ?
                             NULL : &fake_stack_save, to->stack, to->stack_size);
          siglongjmp(to->env, action);
      }
  
      finish_switch_fiber(fake_stack_save);
  
      return ret;
  }
  
  Coroutine *qemu_coroutine_self(void)
  {
      if (!current) {
          current = &leader.base;
      }
      return current;
  }
  
  bool qemu_in_coroutine(void)
  {
      return current && current->caller;
  }
  