请问pxNewTCB->pxStack 是栈底还是整个堆栈？

#if( ( configCHECK_FOR_STACK_OVERFLOW > 1 ) || ( configUSE_TRACE_FACILITY == 1 ) || ( INCLUDE_uxTaskGetStackHighWaterMark == 1 ) )
    {
        /* Fill the stack with a known value to assist debugging. */
        ( void ) memset( pxNewTCB->pxStack, ( int ) tskSTACK_FILL_BYTE, ( size_t ) ulStackDepth * sizeof( StackType_t ) );    //1如果使能了堆栈的溢出检测功能或者追踪功能的话使用一个定值tskSTACK_FILL_BYTE来填充任务堆栈，这个值为0xa5U
    }
    #endif /* ( ( configCHECK_FOR_STACK_OVERFLOW > 1 ) || ( ( configUSE_TRACE_FACILITY == 1 ) || ( INCLUDE_uxTaskGetStackHighWaterMark == 1 ) ) ) */
    /* Calculate the top of stack address.  This depends on whether the stack
    grows from high memory to low (as per the 80x86) or vice versa.
    portSTACK_GROWTH is used to make the result positive or negative as required
    by the port. */
    #if( portSTACK_GROWTH < 0 )
    {
        pxTopOfStack = pxNewTCB->pxStack + ( ulStackDepth - ( uint32_t ) 1 );        //2 计算堆栈栈顶pxTopOfStack初始化任务堆栈的时候用到
     请问pxNewTCB->pxStack 是栈底还是整个堆栈  怎么理解