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Problems with pvPortMalloc/vPortFree

Posted by llapisera on October 31, 2014

Hello.

I have problems when I allocate memory for using as a temporal buffer. My application makes something like this:

MyStruct *p;

p = (MyStruct*)pvPortMalloc(sizeof(MyStruct)); if (p == NULL) { return SOME_ERROR; }

// Use the region allocated

// finally free memory vPortFree((void*)p);

If this is executed one time, there's no problem. But sometimes when memory is freed the data are corrupted (data outside the heap). It seems pvPortMalloc has reserved blocks of memory outside the heap region. Does anyone seen this behavior?

Currently I'm working with heap_4.c and FreeRTOS v7.3.0.

Thanks in advance.


Problems with pvPortMalloc/vPortFree

Posted by rtel on October 31, 2014

The most likely cause is a good old fashioned memory corruption.

When a block is allocated a structure is placed at the start of the block that notes the length of the block. The value returned by pvPortMalloc() jumps over the structure, so the application writer should never see or access it, or even know it is there.

vPortFree() uses the structure to know how to free the memory. It is likely that the information in the structure has been overwritten by something, causing the memory to be freed incorrectly.

Recent FreeRTOS versions include a configASSERT() statement to test for that occurring (as far as is possible), but as you are using an older version it might be that the assert() is not present in your code.

Regards.


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