topic Re: Realloc problems in 8-bit Microcontrollers

Realloc problems

mimais — Thu, 04 Jun 2009 14:38:08 GMT

Dear All,

I am developing with a flexis QE64 with Codewarrior v5.9.0 build 2404 and I experienced some problems with realloc function.

I am using the pre defined function in ALLOC.C (path \CodeWarrior for Microcontrollers V6.1\lib\hc08c\src) and there are some conditions where the reallocation fails.

Either using mutilink P&E or full chip simulation, the following code fails:

In the following piece of code the block where I request a reallocation is 15 bytes and when I call the function realloc((void*) ptr13, 22); the new block is only 5 bytes.

void main(void) {

unsigned char *ptr1, *ptr2, *ptr3, *ptr4, *ptr5, *ptr6, *ptr7, *ptr8, *ptr9, *ptr10, *ptr11, *ptr12, *ptr13, *ptr14;

unsigned char i;

EnableInterrupts; /* enable interrupts */

/* include your code here */

// Build an Heap

ptr1 = malloc(4 * 5 - 5);

ptr2 = malloc(7 * 5 - 5);

ptr3 = malloc(4 * 5 - 5);

ptr4 = malloc(4 * 5 - 5);

ptr5 = malloc(3 * 5 - 5);

ptr6 = malloc(4 * 5 - 5);

ptr7 = malloc(5 * 5 - 5);

ptr8 = malloc(7 * 5 - 5);

ptr9 = malloc(7 * 5 - 5);

ptr10 = malloc(3 * 5 - 5);

ptr11 = malloc(9 * 5 - 5);

ptr12 = malloc(14 * 5 - 5);

ptr13 = malloc(5 * 5 - 5);

ptr14 = malloc(7 * 5 - 5);

free(ptr4);

ptr4 = malloc(3 * 5 - 5);

free(ptr13);

ptr13 = malloc(4 * 5 - 5);

free(ptr12);

// fill the space

for(i = 0; i < 15; i++){

*(ptr13 + i) = i + 1;

}

realloc((void*) ptr13, 22);

for(; {

__RESET_WATCHDOG(); /* feeds the dog */

} /* loop forever */

Can someone help me?

Thanks in advance.

Re: Realloc problems

CrasyCat — Thu, 04 Jun 2009 16:16:35 GMT

Hello

I did check the ANSI C standard and I found that

Notes

If ptr does not match a pointer earlier returned by calloc, malloc, or realloc, or if the space has been deallocated by a call to free or realloc, the behaviour is undefined"

May be you should not free the memory block first.

CrasyCat

Re: Realloc problems

Lundin — Thu, 04 Jun 2009 16:44:08 GMT

Does realloc return NULL or 5 or something else?

Re: Realloc problems

Lundin — Thu, 04 Jun 2009 16:51:25 GMT

Huh? That isn't the case here. That ptr13 was previously freed doesn't matter, malloc() is called for it after that:

ptr13 = malloc(4 * 5 - 5);

...

realloc((void*) ptr13, 22);

Btw ANSI C has been obsolete since 1990, the standard is ISO C.

Message Edited by Lundin on 2009-06-04 11:52 AM

Re: Realloc problems

mimais — Thu, 04 Jun 2009 20:20:34 GMT

For Lundin:

The realloc function returns the pointer of the new re-allocated block. From the return point of view the reallocation succeeded but the size of the reallocated block is only 5 and not 22 (or 25) as requested.

For CrasyCat:

The realloc has been called with a valid block pointer, the area has not been freed!

Thanks.

Re: Realloc problems

Lundin — Thu, 04 Jun 2009 20:47:08 GMT

If it returns a pointer and you get something else than 1 2 3... 15 followed by 7 rubbish values, then something fishy is indeed going on. However, how do you know only 5 bytes were allocated? With the sample code you posted only, it is impossible to tell how much of the data that is valid.

Re: Realloc problems

mimais — Thu, 04 Jun 2009 21:21:36 GMT

Using the full chip simulation tool in Codewarrior I saw, at the end of reallocation, that at the returned address (the realloc returned address) there was only 1 2 3 4 5 and then another heap header block started.

Attached you can find two pictures with the heap status before and after the realloc call.

Note that ptr13 = 0x026E (the block where the realloc has been called) and dest = 0x0228 (the returned block).

If you want I can give to you the all project.