division by 0

[michele]

Hello,
during my work I found that cppcheck doesn't detect me a possible fault: in this part of my code there is a division without any check done before in case the variable is null .. is there a way to force in cppcheck a verification of this condition?
thanks
michele

..
int zBlockSize;
int *pzNumBlocks;

zBlockSize = HalDaf_GetSectorSize();

/ evaluate number of sectors /
if (pzNumBlocks != NULL)
{
*pzNumBlocks =( ( MemSize ) / zBlockSize );
}
..

[michele]

I checked and I found that if I do like that cppcheck detects the division by 0. In my case the problem is more that the return of the function HalDaf_GetSectorSize() is unknown so it could be 0 .. and that check is not done. Is there a way to enable a check for that?
Thanks for the support
Michele

  U16 zDiv = 0u;
  U16 zTest = 16u;

  zTest = zTest/zDiv;

[Daniel Marjamäki]

Thanks! This is a very good forum topic imho.

Is there a way to enable a check for that?

I don't think it's a good idea to add a more noisy check that assumes that functions can return 0. So there is no quick and simple solution imho.

I think it would be a good idea to make Cppcheck more clever about functions return values. Perhaps you should be able to configure that for instance HalDaf_GetSectorSize() can return 0.

Some standard functions such as strchr can return NULL. But I don't want to automatically guess that each strchr() return value is possibly NULL. I would like to guess that the return value can be NULL unless when the arguments mean that it can't be NULL. How we implement this .. I don't know.

Do you know for sure that HalDaf_GetSectorSize() in your code can return zero? I don't know.. but it sounds to me that in general sector sizes can't be 0. Is there any way for Cppcheck to see that this could happen through whole program analysis etc?

[michele]

Hello,
thanks for your reply: I understand your point. I would like to be able to define a rule that every division by zero must be checked by and if divisor != 0, unless the divisor is a constant or a define (so the value is fixed). Is there a way to do that?
Thanks for your support
Michele

[Daniel Marjamäki]

To start with.. can you try ublinter.

https://github.com/danmar/ublinter

let me know if you have problems etc..

it is supposed to be more noisy.

I would like to be able to define a rule that every division by zero must be checked by and if divisor != 0, unless the divisor is a constant or a define (so the value is fixed).

I don't want to have such rule in the cppcheck tool. As an addon or extra rule it would be ok.

Is there a way to do that?

There is no quick and simple way.

The way I would do this is to first improve the ValueFlow::Value so it can say for instance what the min/max values are also. The valueFlowAfterAssign() should set the min/max values. And the valueFlowForward() must probably have some handling for these.

Then I would make sure that these min/max values can be read in the --dump output.

Then I would write a addon that checks for division by zero using the min/max values.

Updating the ValueFlow is the hard part. Improving the --dump output and writing the addon will then be trivial.

[Daniel Marjamäki]

ublinter warns for your original code.

divzero.c:

void f() {
  int zBlockSize;
  int *pzNumBlocks;

  zBlockSize = HalDaf_GetSectorSize();

  /* evaluate number of sectors */
  if (pzNumBlocks != NULL) {
    *pzNumBlocks =( ( MemSize ) / zBlockSize );
  }
}

command line:

$ cppcheck --dump divzero.c
Checking divzero.c...
$ python ublinter.py divzero.c.dump
Checking divzero.c.dump...
[divzero.c:10] Division by zero

[michele]

Thanks a lot, I will have a look.
I'm using cppcheck on my team and other colleagues are using instead klockwork. I'm checking issues not detected by cppcheck .. and viceversa. :)
Thanks again for the support