[BUG] Stack could be unaligned if portSTACK_GROWTH > 0

[ivq]

The stack of a task could not be properly aligned if stack grows upwards(portSTACK_GROWTH > 0).

Possible call trace of the bug:

1. xTaskCreateStatic() creates a task, given stack buffer is only aligned as StackType_t.
2. prvInitialiseNewTask() initializes the task, including the stack. The current implementation does not align the stack for portSTACK_GROWTH > 0. If portBYTE_ALIGNMENT is stricter than that of StackType_t, this will lead to unaligned stack or assert error if configASSERT is enabled.

Target None. The bug is only theoretically possible.

Host Not applicable.

To Reproduce Not applicable.

Expected behavior The stack should be aligned as portSTACK_GROWTH < 0 does.

Proposed Fix https://github.com/FreeRTOS/FreeRTOS-Kernel/pull/751

[aggarg]

If portBYTE_ALIGNMENT is stricter than that of StackType_t

StackType_t is always defined according to the portBYTE_ALIGNMENT. The following are the 4 ports for which portSTACK_GROWTH > 0:

1. portable\ThirdParty\Community-Supported-Ports\CCS\C2000_C28x

   #define portSTACK_TYPE  uint16_t
   #define portBYTE_ALIGNMENT      2

2. portable\SDCC\Cygnal

   #define portSTACK_TYPE  uint8_t
   #define portBYTE_ALIGNMENT          1

3. portable\MPLAB\PIC24_dsPIC

   #define portSTACK_TYPE  uint16_t
   #define portBYTE_ALIGNMENT          2

4. portable\MPLAB\PIC18F\portmacro.h

   #define portSTACK_TYPE  uint8_t
   #define portBYTE_ALIGNMENT          1

Therefore, no special alignment related adjustment is needed. Even if a new port defines the StackType_t incorrectly, the assert will catch it.

[ivq]

Yes, for all current ports for which portSTACK_GROWTH > 0, that's true. But I don't see any requirement on the binding of portBYTE_ALIGNMENT and StackType_t. Many ports for which portSTACK_GROWTH < 0 don't satisfy the requirement. For example:

1. portable/IAR/ARM_CM4F/portmacro.h

   #define portBYTE_ALIGNMENT    8
   #define portSTACK_TYPE    uint32_t

2. portable/GCC/RISC-V/portmacro.h

   // RV64, non E extension
   #define portBYTE_ALIGNMENT      16
   #define portSTACK_TYPE          uint64_t

The patch is indeed for future new ports.

[aggarg]

The patch is indeed for future new ports.

Okay, that is reasonable.