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Re: An idea for heap-checking stuffs [message #15692 is a reply to message #15690]

Sun, 04 May 2008 20:13

mirek
Messages: 14263
Registered: November 2005

Ultimate Member

mdelfede wrote on Sun, 04 May 2008 12:45

luzr wrote on Sun, 04 May 2008 18:23

mdelfede wrote on Sun, 04 May 2008 06:06

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.

Good idea to actviate heap checks in release mode.

Quote:

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.

This is already done (in debug mode).

Yes ? before and after the returned pointer ? that's good !

Quote:

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.

Yep, this is also done Wink

BTW, I am using these links as sentinels. And it is also used to check leaks.

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

MemoryCheck.

mhhhh... as far as I could see, MemoryCheck does a check on freed blocks, and only on small allocs... or am I wrong ?
Does it check also allocated blocks integrity ?

Sorry, it is in fact "MemoryCheckDebug". It calls basic MemoryCheck and then goes through the list.

Quote:

That's very interesting... but how do you see the serial number and how do you set breakpoint ?

You should see breakpoint serial number in the .log.

You can set it using "MemoryBreakpoint" function or using --memory_breakpoint commandline option. However, this is not very helpful in our Ubuntu problem as both can get active only AppInit...

Mirek

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