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An idea for heap-checking stuffs [message #15678]

Sun, 04 May 2008 12:06

mdelfede
Messages: 1307
Registered: September 2007

Ultimate Contributor

After last bug (still unresolved) of memory corruption on upp compiled under ubuntu hardy, I was thinking about some heap checking stuffs that IMO could be incorporated in upp.
So, the idea (I don't know if somebody already did it!) :

1) Set up a new building flag, for example HEAPCHECK.
2) when code is compiled with HEAPCHECK, do the following:

3) On each dynamic allocation, reserve some more bytes, some before and some after returned pointer, and fill with known data.
For example, if I need 10 bytes, I could reserve 20, like this :

DDDDDAAAAAAAAAADDDDD
     |
returned pointer here

DDDDD represent the 'spare' allocated bytes, filled with known values.

4) Keep a linked list not only for freed data but also for allocated data. I know that this can slow down much the code, but.... it's just when needed for debugging.

5) create 2 functions, FreeCheck() and UsedCheck() that scans the free and used allocated space and checks for values on DDDDD fileds.

6) allow the ability to switch on/off the heap checking on each allocation/free of memory. That one would slow down much the code, but would also allow to find corruptions just a little after they happens.

Up to here, not much work in upp code, IMHO.
The best would also be to add

7) Add container's methods entry/exit pointer checking. So, for each method called for a container, check container's pointers on method entry and exit. That one would catch 99% of pointer misusage as soon as it happens. Of course, that last one would mean to add a lot of (conditional) code to upp core.

Ciao

Max

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