How to resolve observed warning when -Wcast-align flag is used during compile time

[rxa1031]

Hi,

On using compiler flag -Wcast-align below errors are observed in stm32h7xx_hal_uart.c , tm32h7xx_hal_uart_ex.c and ethernetif.c files.

C:/ST/Repository/STM32Cube_FW_H7_V1.12.1/Drivers/STM32H7xx_HAL_Driver/Src/stm32h7xx_hal_uart.c: In function 'HAL_UART_Transmit':
C:/ST/Repository/STM32Cube_FW_H7_V1.12.1/Drivers/STM32H7xx_HAL_Driver/Src/stm32h7xx_hal_uart.c:1147:21: warning: cast increases required alignment of target type [-Wcast-align]
 1147 |       pdata16bits = (const uint16_t *) pData;
      |                     ^
C:/ST/Repository/STM32Cube_FW_H7_V1.12.1/Drivers/STM32H7xx_HAL_Driver/Src/stm32h7xx_hal_uart.c: In function 'HAL_UART_Receive':
C:/ST/Repository/STM32Cube_FW_H7_V1.12.1/Drivers/STM32H7xx_HAL_Driver/Src/stm32h7xx_hal_uart.c:1243:21: warning: cast increases required alignment of target type [-Wcast-align]
 1243 |       pdata16bits = (uint16_t *) pData;
      |                     ^
C:/ST/Repository/STM32Cube_FW_H7_V1.12.1/Drivers/STM32H7xx_HAL_Driver/Src/stm32h7xx_hal_uart.c: In function 'UART_TxISR_16BIT':
C:/ST/Repository/STM32Cube_FW_H7_V1.12.1/Drivers/STM32H7xx_HAL_Driver/Src/stm32h7xx_hal_uart.c:4107:13: warning: cast increases required alignment of target type [-Wcast-align]
 4107 |       tmp = (const uint16_t *) huart->pTxBuffPtr;
      |             ^
C:/ST/Repository/STM32Cube_FW_H7_V1.12.1/Drivers/STM32H7xx_HAL_Driver/Src/stm32h7xx_hal_uart.c: In function 'UART_TxISR_16BIT_FIFOEN':
C:/ST/Repository/STM32Cube_FW_H7_V1.12.1/Drivers/STM32H7xx_HAL_Driver/Src/stm32h7xx_hal_uart.c:4184:15: warning: cast increases required alignment of target type [-Wcast-align]
 4184 |         tmp = (const uint16_t *) huart->pTxBuffPtr;
      |               ^
C:/ST/Repository/STM32Cube_FW_H7_V1.12.1/Drivers/STM32H7xx_HAL_Driver/Src/stm32h7xx_hal_uart.c: In function 'UART_RxISR_16BIT':
C:/ST/Repository/STM32Cube_FW_H7_V1.12.1/Drivers/STM32H7xx_HAL_Driver/Src/stm32h7xx_hal_uart.c:4329:11: warning: cast increases required alignment of target type [-Wcast-align]
 4329 |     tmp = (uint16_t *) huart->pRxBuffPtr ;
      |           ^
C:/ST/Repository/STM32Cube_FW_H7_V1.12.1/Drivers/STM32H7xx_HAL_Driver/Src/stm32h7xx_hal_uart.c: In function 'UART_RxISR_16BIT_FIFOEN':
C:/ST/Repository/STM32Cube_FW_H7_V1.12.1/Drivers/STM32H7xx_HAL_Driver/Src/stm32h7xx_hal_uart.c:4593:13: warning: cast increases required alignment of target type [-Wcast-align]
 4593 |       tmp = (uint16_t *) huart->pRxBuffPtr ;
      |             ^
C:/ST/Repository/STM32Cube_FW_H7_V1.12.1/Drivers/STM32H7xx_HAL_Driver/Src/stm32h7xx_hal_uart_ex.c: In function 'HAL_UARTEx_ReceiveToIdle':
C:/ST/Repository/STM32Cube_FW_H7_V1.12.1/Drivers/STM32H7xx_HAL_Driver/Src/stm32h7xx_hal_uart_ex.c:748:21: warning: cast increases required alignment of target type [-Wcast-align]
  748 |       pdata16bits = (uint16_t *) pData;
      |                     ^
D:/IMPORTANT_CODES/KEIL_plus_STM32CUBEIDE/lwIP_Ethernet/Src/ethernetif.c: In function 'HAL_ETH_RxLinkCallback':
D:/IMPORTANT_CODES/KEIL_plus_STM32CUBEIDE/lwIP_Ethernet/Src/ethernetif.c:750:7: warning: cast increases required alignment of target type [-Wcast-align]
  750 |   p = (struct pbuf *)(buff - offsetof(RxBuff_t, buff));
      |       ^
D:/IMPORTANT_CODES/KEIL_plus_STM32CUBEIDE/lwIP_Ethernet/Src/ethernetif.c:776:32: warning: cast increases required alignment of target type [-Wcast-align]
  776 |   SCB_InvalidateDCache_by_Addr((uint32_t *)buff, Length);

I request a suggestion on how to resolve the concern without removing the compiler flag -Wcast-align.
As these files are coded by ST, and are added to project when the code is generated using STM32CubeMX, I am unable to use code similar to below to remove the observed warnings:

Option 1:
Cast argument passed to function to const void * instead of const uint8_t *
like:
HAL_StatusTypeDef HAL_UART_Transmit(UART_HandleTypeDef *huart, const void *pData, uint16_t Size, uint32_t Timeout)

Option 2:
Use pdata16bits = (uint16_t *)__builtin_assume_aligned(pData, 2); or similar in place of pdata16bits = (const uint16_t *) pData;

Option 3:

typedef union {
	uint8_t *puc;
	uint16_t *pu16;
} pDataTypeDef;
pDataTypeDef pDataUnion;
pDataUnion.puc = pData;
    /* In case of 9bits/No Parity transfer, pRxData needs to be handled as a uint16_t pointer */
    if ((huart->Init.WordLength == UART_WORDLENGTH_9B) && (huart->Init.Parity == UART_PARITY_NONE))
    {
      pdata8bits  = NULL;
      pdata16bits = (uint16_t *) pDataUnion.pu16;
    }
    else
    {
      pdata8bits  = pData;
      pdata16bits = NULL;
    }

in place of:

    /* In case of 9bits/No Parity transfer, pRxData needs to be handled as a uint16_t pointer */
    if ((huart->Init.WordLength == UART_WORDLENGTH_9B) && (huart->Init.Parity == UART_PARITY_NONE))
    {
      pdata8bits  = NULL;
      pdata16bits = (uint16_t *) pData;
    }
    else
    {
      pdata8bits  = pData;
      pdata16bits = NULL;
    }

Please suggest how to fix the issue.

Thanks!
Rajeev

[rxa1031]

Hi,

I am using below compile time and link time flags:

Regards,
Rajeev