Memory related errors

Question

Hello,

I mostly work on C language for my work. I have faced many issues and spent lot time in debugging issues related to dynamically allocated memory corruption/overwriting. Like malloc(A) A bytes but use write more than A bytes. Towards that i was trying to read few things when i read about :-

1.) An approach wherein one allocates more memory than what is needed. And write some known value/pattern in that extra locations. Then during program execution that pattern should be untouched, else it indicated memory corruption/overwriting. But how does this approach work. Does it mean for every write to that pointer which is allocated using malloc() i should be doing a memory read of the additional sentinel pattern and read for its sanity? That would make my whole program very slow. And to say that we can remove these checks from the release version of the code, is also not fruitful as memory related issues can happen more in 'real scenario'. So can we handle this?

2.) I heard that there is something called HEAP WALKER, which enables programs to detect memory related issues? How can one enable this.

thank you.

-AD.

Answer 1

Memory guards can catch some heap corruption. It is slower (especially deallocations) but it's just for debug purposes and your release build would not include this.

Heap walking is platform specific, but not necessarily too useful. The simplest check is simply to wrap your allocations and log them to a file with the LINE and FILE information for your debug mode, and most any leaks will be apparent very quickly when you exit the program and numbers don't tally up.

Search google for LINE and I am sure lots of results will show up.

Answer 2

If you're working under Linux or OSX, have a look at Valgrind (free, available on OSX via Macports). For Windows, we're using Rational PurifyPlus (needs a license).

You can also have a look at Dmalloc or even at Paul Nettle's memory manager which helps tracking memory allocation related bugs.

Answer 3

If you're on Mac OS X, there's an awesome library called libgmalloc. libgmalloc places each memory allocation on a separate page. Any memory access/write beyond the page will immediately trigger a bus error. Note however that running your program with libgmalloc will likely result in a significant slowdown.