c - ST Micro HAL, stm32f7xx_hal_crc.c 如何解决【警告】取消引用类型双关指针会破坏严格别名规则
问题描述
在 STM32Cube_FW_F7_V1.3.0 和仍然在 STM32Cube_FW_F7_V1.11.0
使用 -Os 或 -O2 编译 stm32f7 HAL 库时收到以下警告。
注意：-O1 编译时没有警告。
[Warning] dereferencing type-punned pointer will break strict-aliasing rules
警告是有道理的。该代码似乎可以正常工作。但是，我想将警告视为错误。
问题：如何在不破坏 crc 模块的情况下更改代码以删除警告？
注意：我在网上的任何地方都找不到解决方案。
这是导致警告的行之一
*(__IO uint16_t*) (&hcrc->Instance->DR) = (uint16_t)(((uint16_t)(pBuffer[4*i])<<8) | (uint16_t)(pBuffer[4*i+1]));
我相信这有点棘手和令人生畏，因为它正在处理硬件 crc 寄存器。
这是 ST Micro 的许可证，其中规定我在分发源代码时必须包含，它与问题无关
/******************************************************************************
* @attention
*
* <h2><center>© COPYRIGHT(c) 2015 STMicroelectronics</center></h2>
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
* 3. Neither the name of STMicroelectronics nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
******************************************************************************
*/
相关代码：
#define __IO volatile /*!< Defines 'read / write' permissions */
typedef struct
{
__IO uint32_t DR; /*!< CRC Data register, Address offset: 0x00 */
__IO uint8_t IDR; /*!< CRC Independent data register, Address offset: 0x04 */
uint8_t RESERVED0; /*!< Reserved, 0x05 */
uint16_t RESERVED1; /*!< Reserved, 0x06 */
__IO uint32_t CR; /*!< CRC Control register, Address offset: 0x08 */
uint32_t RESERVED2; /*!< Reserved, 0x0C */
__IO uint32_t INIT; /*!< Initial CRC value register, Address offset: 0x10 */
__IO uint32_t POL; /*!< CRC polynomial register, Address offset: 0x14 */
} CRC_TypeDef;
/**
* @brief Enter 8-bit input data to the CRC calculator.
* Specific data handling to optimize processing time.
* @param hcrc: CRC handle
* @param pBuffer: pointer to the input data buffer
* @param BufferLength: input data buffer length
* @retval uint32_t CRC (returned value LSBs for CRC shorter than 32 bits)
*/
static uint32_t CRC_Handle_8(CRC_HandleTypeDef *hcrc, uint8_t pBuffer[], uint32_t BufferLength)
{
uint32_t i = 0; /* input data buffer index */
/* Processing time optimization: 4 bytes are entered in a row with a single word write,
* last bytes must be carefully fed to the CRC calculator to ensure a correct type
* handling by the IP */
for(i = 0; i < (BufferLength/4); i++)
{
hcrc->Instance->DR = (uint32_t)(((uint32_t)(pBuffer[4*i])<<24) | ((uint32_t)(pBuffer[4*i+1])<<16) | ((uint32_t)(pBuffer[4*i+2])<<8) | (uint32_t)(pBuffer[4*i+3]));
}
/* last bytes specific handling */
if((BufferLength%4) != 0)
{
if(BufferLength%4 == 1)
{
*(__IO uint8_t*) (&hcrc->Instance->DR) = pBuffer[4*i];
}
if(BufferLength%4 == 2)
{
//the following line gives the warning (rightfully) '[Warning] dereferencing type-punned pointer will break strict-aliasing rules'
*(__IO uint16_t*) (&hcrc->Instance->DR) = (uint16_t)(((uint16_t)(pBuffer[4*i])<<8) | (uint16_t)(pBuffer[4*i+1]));
}
if(BufferLength%4 == 3)
{
//the following line gives the warning (rightfully) '[Warning] dereferencing type-punned pointer will break strict-aliasing rules'
*(__IO uint16_t*) (&hcrc->Instance->DR) = (uint16_t)(((uint16_t)(pBuffer[4*i])<<8) | (uint16_t)(pBuffer[4*i+1]));
*(__IO uint8_t*) (&hcrc->Instance->DR) = pBuffer[4*i+2];
}
}
/* Return the CRC computed value */
return hcrc->Instance->DR;
}
警告也出现在 16 位 CRC 函数中
解决方案
使用匿名联合来避免 c 类型双关语。
更改CRC_TypeDef头文件中的定义以使用匿名联合。
typedef struct
{
union
{
__IO uint32_t DR; /*!< CRC Data register 32 bit access, Address offset: 0x00 */
__IO uint16_t DR16; /*!< CRC Data register 16 bit access, Address offset: 0x00 */
__IO uint8_t DR8; /*!< CRC Data register 8 bit access, Address offset: 0x00 */
};
__IO uint8_t IDR; /*!< CRC Independent data register, Address offset: 0x04 */
uint8_t RESERVED0; /*!< Reserved, 0x05 */
uint16_t RESERVED1; /*!< Reserved, 0x06 */
__IO uint32_t CR; /*!< CRC Control register, Address offset: 0x08 */
uint32_t RESERVED2; /*!< Reserved, 0x0C */
__IO uint32_t INIT; /*!< Initial CRC value register, Address offset: 0x10 */
__IO uint32_t POL; /*!< CRC polynomial register, Address offset: 0x14 */
} CRC_TypeDef;
CRC_Handle_8在andCRC_Handle_16函数中使用这个新的联合。
/**
* @brief Enter 8-bit input data to the CRC calculator.
* Specific data handling to optimize processing time.
* @param hcrc: CRC handle
* @param pBuffer: pointer to the input data buffer
* @param BufferLength: input data buffer length
* @retval uint32_t CRC (returned value LSBs for CRC shorter than 32 bits)
*/
static uint32_t CRC_Handle_8(CRC_HandleTypeDef *hcrc, uint8_t pBuffer[], uint32_t BufferLength)
{
uint32_t i = 0; /* input data buffer index */
/* Processing time optimization: 4 bytes are entered in a row with a single word write,
* last bytes must be carefully fed to the CRC calculator to ensure a correct type
* handling by the IP */
for(i = 0; i < (BufferLength/4); i++)
{
hcrc->Instance->DR = (uint32_t)(((uint32_t)(pBuffer[4*i])<<24) | ((uint32_t)(pBuffer[4*i+1])<<16) | ((uint32_t)(pBuffer[4*i+2])<<8) | (uint32_t)(pBuffer[4*i+3]));
}
/* last bytes specific handling */
if((BufferLength%4) != 0)
{
if(BufferLength%4 == 1)
{
hcrc->Instance->DR8 = pBuffer[4*i];
}
if(BufferLength%4 == 2)
{
hcrc->Instance->DR16 = (uint16_t)(((uint16_t)(pBuffer[4*i])<<8) | (uint16_t)(pBuffer[4*i+1]));
}
if(BufferLength%4 == 3)
{
hcrc->Instance->DR16 = (uint16_t)(((uint16_t)(pBuffer[4*i])<<8) | (uint16_t)(pBuffer[4*i+1]));
hcrc->Instance->DR8 = pBuffer[4*i+2];
}
}
/* Return the CRC computed value */
return hcrc->Instance->DR;
}
/**
* @brief Enter 16-bit input data to the CRC calculator.
* Specific data handling to optimize processing time.
* @param hcrc: CRC handle
* @param pBuffer: pointer to the input data buffer
* @param BufferLength: input data buffer length
* @retval uint32_t CRC (returned value LSBs for CRC shorter than 32 bits)
*/
static uint32_t CRC_Handle_16(CRC_HandleTypeDef *hcrc, uint16_t pBuffer[], uint32_t BufferLength)
{
uint32_t i = 0; /* input data buffer index */
/* Processing time optimization: 2 HalfWords are entered in a row with a single word write,
* in case of odd length, last HalfWord must be carefully fed to the CRC calculator to ensure
* a correct type handling by the IP */
for(i = 0; i < (BufferLength/2); i++)
{
hcrc->Instance->DR = (((uint32_t)(pBuffer[2*i])<<16) | (uint32_t)(pBuffer[2*i+1]));
}
if((BufferLength%2) != 0)
{
hcrc->Instance->DR16 = pBuffer[2*i];
}
/* Return the CRC computed value */
return hcrc->Instance->DR;
}
强制性 ST Micro 许可和免责声明。
******************************************************************************
* @attention
*
* <h2><center>© COPYRIGHT(c) 2015 STMicroelectronics</center></h2>
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
* 3. Neither the name of STMicroelectronics nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
******************************************************************************
*/
感谢 Olaf 在评论中暗示了这个答案。
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