在RT-Thread在不使能RT_USING_USER_MAIN时，main函数中定义的局部变量地址范围是多少？

最近在使用RT-Thread时发现，在不使能RT_USING_USER_MAIN时，在main函数中定义局部变量，该变量所在栈与线程所在栈存在重合情况。

复现步骤：

不使能RT_USING_USER_MAIN；
在main函数中定义非static、非heap变量data;
将data地址传入线程data_print_thread，在data_print_thread中反复给data赋值并打印观测data值；
观测到data的值在被传入不久后就被其它地方修改了；打印输出如下：
data address: 0x2042EFA4, 0x2042EFA5, 0x2042EFA4
data before assignment: 168, 239
data after assignment one: 3, 4
data after assignment two: 168, 239

问：

在RT-Thread在不使能RT_USING_USER_MAIN时，main函数中定义的局部变量地址范围是多少？
怎么知道data的值是被什么修改的？
main.c的源码如下：

#include <rthw.h>
#include <rtthread.h>
#include <stdint.h>
#include "bsp.h"
typedef struct {
uint8_t a;
uint8_t b;
uint8_t a1[82]; // 定义这个变量使得a, b的地址到某个指定位置，便于观察到a,b值被修改，
//当a1容量为2或1000时，a,b的值不会被修改，不好观测。
} app_param;
void data_assign_print_thread(void* param) {
app_param* app_init = reinterpret_cast<app_param*>(param);
while (1) {
rt_kprintf("data address: 0x%08X, 0x%08X, 0x%08X\n", &app_init->a,
&app_init->b, app_init);
rt_kprintf("data before assignment: %d, %d\n", app_init->a, app_init->b);
app_init->a = 3;
app_init->b = 4;
rt_kprintf("data after assignment one: %d, %d\n", app_init->a, app_init->b);
rt_kprintf("data after assignment two: %d, %d\n\n", app_init->a, app_init->b);
rt_thread_delay(1000);
}
}
void rt_application_init(void* param) {
rt_thread_t tid;
tid = rt_thread_create("data_assign_print_thread", data_assign_print_thread, param,
1024 * 2, 1, 2000);
RT_ASSERT(tid != RT_NULL);
rt_thread_startup(tid);
}
int main(void) {
rt_hw_interrupt_disable();
/* board level initialization

NOTE: please initialize heap inside board initialization./
rt_hw_board_init();
/ show RT-Thread version /
rt_show_version();
/ timer system initialization /
rt_system_timer_init();
/ scheduler system initialization /
rt_system_scheduler_init();
/ create init_thread /
app_param app_tasks_param;
rt_application_init(&app_tasks_param);
/ timer thread initialization /
rt_system_timer_thread_init();
/ idle thread initialization /
rt_thread_idle_init();
/ start scheduler /
rt_system_scheduler_start();
/ never reach here */
return 0;
}