/*
* SPDX-FileCopyrightText: 2015-2021 Espressif Systems (Shanghai) CO LTD
*
* SPDX-License-Identifier: Apache-2.0
*/
#include <stdlib.h>
#include <assert.h>
#include <cxxabi.h>
#include <stdint.h>
#include <limits.h>
#include <algorithm>
#include <sys/lock.h>
#include "freertos/FreeRTOS.h"
#include "freertos/semphr.h"
#include "freertos/task.h"
using __cxxabiv1::__guard;
static SemaphoreHandle_t s_static_init_mutex = NULL; //!< lock used for the critical section
static SemaphoreHandle_t s_static_init_wait_sem = NULL; //!< counting semaphore used by the waiting tasks
static portMUX_TYPE s_init_spinlock = portMUX_INITIALIZER_UNLOCKED; //!< spinlock used to guard initialization of the above two primitives
static size_t s_static_init_waiting_count = 0; //!< number of tasks which are waiting for static init guards
#ifndef _NDEBUG
static size_t s_static_init_max_waiting_count = 0; //!< maximum ever value of the above; can be inspected using GDB for debugging purposes
#endif
extern "C" int __cxa_guard_acquire(__guard* pg);
extern "C" void __cxa_guard_release(__guard* pg) throw();
extern "C" void __cxa_guard_abort(__guard* pg) throw();
extern "C" void __cxa_guard_dummy(void);
/**
* Layout of the guard object (defined by the ABI).
*
* Compiler will check lower byte before calling guard functions.
*/
typedef struct {
uint8_t ready; //!< nonzero if initialization is done
uint8_t pending; //!< nonzero if initialization is in progress
} guard_t;
static void static_init_prepare()
{
portENTER_CRITICAL(&s_init_spinlock);
if (s_static_init_mutex == NULL) {
s_static_init_mutex = xSemaphoreCreateMutex();
s_static_init_wait_sem = xSemaphoreCreateCounting(INT_MAX, 0);
if (s_static_init_mutex == NULL || s_static_init_wait_sem == NULL) {
// no way to bail out of static initialization without these
abort();
}
}
portEXIT_CRITICAL(&s_init_spinlock);
}
/**
* Use s_static_init_wait_sem to wait until guard->pending == 0.
* Preconditions:
* - s_static_init_mutex taken
* - guard.pending == 1
* Postconditions:
* - s_static_init_mutex taken
* - guard.pending == 0
*/
static void wait_for_guard_obj(guard_t* g)
{
s_static_init_waiting_count++;
#ifndef _NDEBUG
s_static_init_max_waiting_count = std::max(s_static_init_waiting_count,
s_static_init_max_waiting_count);
#endif
do {
auto result = xSemaphoreGive(s_static_init_mutex);
assert(result);
static_cast<void>(result);
/* Task may be preempted here, but this isn't a problem,
* as the semaphore will be given exactly the s_static_init_waiting_count
* number of times; eventually the current task will execute next statement,
* which will immediately succeed.
*/
result = xSemaphoreTake(s_static_init_wait_sem, portMAX_DELAY);
assert(result);
/* At this point the semaphore was given, so all waiting tasks have woken up.
* We take s_static_init_mutex before accessing the state of the guard
* object again.
*/
result = xSemaphoreTake(s_static_init_mutex, portMAX_DELAY);
assert(result);
/* Semaphore may have been given because some other guard object became ready.
* Check the guard object we need and wait again if it is still pending.
*/
} while(g->pending);
s_static_init_waiting_count--;
}
/**
* Unblock tasks waiting for static initialization to complete.
* Preconditions:
* - s_static_init_mutex taken
* Postconditions:
* - s_static_init_mutex taken
*/
static void signal_waiting_tasks()
{
auto count = s_static_init_waiting_count;
while (count--) {
xSemaphoreGive(s_static_init_wait_sem);
}
}
extern "C" int __cxa_guard_acquire(__guard* pg)
{
guard_t* g = reinterpret_cast<guard_t*>(pg);
const auto scheduler_started = xTaskGetSchedulerState() != taskSCHEDULER_NOT_STARTED;
if (!scheduler_started) {
if (g->pending) {
/* Before the scheduler has started, there we don't support simultaneous
* static initialization. This may be implemented using a spinlock and a
* s32c1i instruction, though.
*/
abort();
}
} else {
if (s_static_init_mutex == NULL) {
static_init_prepare();
}
/* We don't need to use double-checked locking pattern here, as the compiler
* must generate code to check if the first byte of *pg is non-zero, before
* calling __cxa_guard_acquire.
*/
auto result = xSemaphoreTake(s_static_init_mutex, portMAX_DELAY);
assert(result);
static_cast<void>(result);
if (g->pending) {
/* Another task is doing initialization at the moment; wait until it calls
* __cxa_guard_release or __cxa_guard_abort
*/
wait_for_guard_obj(g);
/* At this point there are two scenarios:
* - the task which was doing static initialization has called __cxa_guard_release,
* which means that g->ready is set. We need to return 0.
* - the task which was doing static initialization has called __cxa_guard_abort,
* which means that g->ready is not set; we should acquire the guard and return 1,
* same as for the case if we didn't have to wait.
* Note: actually the second scenario is unlikely to occur in the current
* configuration because exception support is disabled.
*/
}
}
int ret;
if (g->ready) {
/* Static initialization has been done by another task; nothing to do here */
ret = 0;
} else {
/* Current task can start doing static initialization */
g->pending = 1;
ret = 1;
}
if (scheduler_started) {
auto result = xSemaphoreGive(s_static_init_mutex);
assert(result);
static_cast<void>(result);
}
return ret;
}
extern "C" void __cxa_guard_release(__guard* pg) throw()
{
guard_t* g = reinterpret_cast<guard_t*>(pg);
const auto scheduler_started = xTaskGetSchedulerState() != taskSCHEDULER_NOT_STARTED;
if (scheduler_started) {
auto result = xSemaphoreTake(s_static_init_mutex, portMAX_DELAY);
assert(result);
static_cast<void>(result);
}
assert(g->pending && "tried to release a guard which wasn't acquired");
g->pending = 0;
/* Initialization was successful */
g->ready = 1;
if (scheduler_started) {
/* Unblock the tasks waiting for static initialization to complete */
signal_waiting_tasks();
auto result = xSemaphoreGive(s_static_init_mutex);
assert(result);
static_cast<void>(result);
}
}
extern "C" void __cxa_guard_abort(__guard* pg) throw()
{
guard_t* g = reinterpret_cast<guard_t*>(pg);
const auto scheduler_started = xTaskGetSchedulerState() != taskSCHEDULER_NOT_STARTED;
if (scheduler_started) {
auto result = xSemaphoreTake(s_static_init_mutex, portMAX_DELAY);
assert(result);
static_cast<void>(result);
}
assert(!g->ready && "tried to abort a guard which is ready");
assert(g->pending && "tried to release a guard which is not acquired");
g->pending = 0;
if (scheduler_started) {
/* Unblock the tasks waiting for static initialization to complete */
signal_waiting_tasks();
auto result = xSemaphoreGive(s_static_init_mutex);
assert(result);
static_cast<void>(result);
}
}
/**
* Dummy function used to force linking this file instead of the same one in libstdc++.
* This works via -u __cxa_guard_dummy flag in component.mk
*/
extern "C" void __cxa_guard_dummy(void)
{
}