Visual Studio (VC++ 2005) Debugging memory

Question

I am chasing a memory heap corruption error. All I have is the memory address that has purportedly been modified after being freed. Windows basically triggers a breakpoint on exit and I see an error message in the Output Window as follows:

HEAP[myprogram.exe]: HEAP: Free Heap block df56c20 modified at df56c80 after it was freed

My question is at the exact point when Windows triggers the breakpoint, can I trace back to the point in my code corresponding to the data associated with this address? That would at least help debug this. Appreciate any ideas on how I could go about doing this. I read http://msdn.microsoft.com/en-us/library/s3aw423e.aspx but it wasn't terribly clear how I could go about doing what I wanted. Thanks!

Luchian Grigore · Accepted Answer · 2012-06-15 22:47:56Z

1

You can set a breakpoint at a memory address. Just go to the breakpoints window and add a new data breakpoint. This can help if you see the corruption happening at the same address for each run.

However with issues like this, the problem is most likely somewhere else. Common causes come from undefined behavior. Look for:

double deletes
not returning from a function
going out of bounds in an array
writing to memory you don't own

answered Jun 15, 2012 at 22:47

Luchian Grigore

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squashed.bugaboo Over a year ago

Thanks @Luchian: I just tried that but by that point, the code seems to be Windows libraries ntdll.dll with no call stack leading back to my application, and the problem is that this address is not fixed with each run; so I don't know its hex-representation a priori. If I knew that a priori I would've put it to begin with before even starting debugging. Any suggestions?

Luchian Grigore Over a year ago

@squashed.bugaboo remove code until you no longer get the corruption. That should narrow it down.

squashed.bugaboo Over a year ago

Thanks @Luchian: OK.. I see, so you are basically suggesting (what I was putting off), to revert back to a working version of the code that didn't have the error. Am I stating you correctly?

Luchian Grigore Over a year ago

@squashed.bugaboo yes, the cause is in the difference between the versions.

squashed.bugaboo Over a year ago

Thanks. OK. I will certainly do that, but to go back to my question tho' is there any utility (3rd party also) that can trace back to application data from a memory address at a Window triggered breakpoint? I've tried Visual Leak Detector. But it happily says there are no leaks on exit and right after that I get the Windows triggered error message. It seems like there should be something around to trace back from memory address in situations like this.

Neeraj Singh · Accepted Answer · 2012-06-16 20:06:28Z

0

Use Application Verifier and enable PageHeap. That will break into the debugger immediately upon corruption of the memory.

answered Jun 16, 2012 at 20:06

Neeraj Singh

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