Trap NULL pointer dereference

[ckw089]

Hi,

We are using STM32H750 for the new product development. The IDE is IAR Embedded Workbench and the RTOS is uC/OS-II.

We found that it is OK to dereference NULL pointer on STM32H750.

Any way to trap NULL pointer dereference to generate an access violation error ?

rgds,

kc Wong

[TDK]

Edit: Oh I misunderstood.

[ckw089]

The address zero is mapped to the ITCM ram.

define symbol __ICFEDIT_region_ITCMR_start__      = 0x00000000;

define symbol __ICFEDIT_region_ITCMR_end__       = 0x0000FFFF;

define symbol __ICFEDIT_region_DTCMR_start__      = 0x20000000;

define symbol __ICFEDIT_region_DTCMR_end__       = 0x2001FFFF;

place in ITCMR_region      { section .textrw };

place in DTCMR_region      { section .dtcm_ram };

And the below code will just execute fine.

 int* p = 0;

 int x = *p;

 x = 0x12345678;

 *p = x;

[Piranha]

Should be able to do it by configuring at least a small memory block at the beginning of ITCM with "no access" in MPU.

[ckw089]

Thanks Piranha, you are right.

In order to catch NULL pointer dereference defects, we shall configure the MPU to no access (or read-only) for the whole ITCMR_region (or the first 1024 bytes).

 MPU_InitStruct.Enable = MPU_REGION_ENABLE;

 MPU_InitStruct.BaseAddress = 0x00000000;

 MPU_InitStruct.Size = MPU_REGION_SIZE_64KB;

  MPU_InitStruct.AccessPermission = MPU_REGION_NO_ACCESS;

  MPU_InitStruct.IsBufferable = MPU_ACCESS_NOT_BUFFERABLE;

 MPU_InitStruct.IsCacheable = MPU_ACCESS_CACHEABLE;

 MPU_InitStruct.IsShareable = MPU_ACCESS_SHAREABLE;

 MPU_InitStruct.Number = MPU_REGION_NUMBER1;

 MPU_InitStruct.TypeExtField = MPU_TEX_LEVEL0;

 MPU_InitStruct.SubRegionDisable = 0x00;

 MPU_InitStruct.DisableExec = MPU_INSTRUCTION_ACCESS_DISABLE;

 HAL_MPU_ConfigRegion(&MPU_InitStruct);