Re: Detecting freed memory
- From: Keith Thompson <kst-u@xxxxxxx>
- Date: Thu, 01 Sep 2005 19:39:49 GMT
"EventHelix.com" <eventhelix@xxxxxxxxx> writes:
> There is no general way to do this.
To do what? Please provide context; don't assume that your readers
can easily see the parent article, or even the subject header.
If you want to post a followup via groups.google.com, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers.
The parent article asked about how to detect, after a call to free(p),
that p is no longer a valid pointer. (Quick answer: you can't.)
> One way is to write your own
> wrappers around malloc and free and include different signatures in the
> buffer that can be checked.
>
> Microsoft Visual C++ compiler does something similar in a Debug build.
> When a buffer is freed, it copies a known signature pattern in all the
> bytes of the buffer.
It would also have to initialize newly malloc()ed memory with some
other pattern. Also, it can't easily handle cases like this:
p1 = malloc(SOME_SIZE);
...
free(p1);
...
p2 = malloc(SOME_SIZE);
After the second malloc(), p2 might very well point to the same chunk
of memory that p1 pointed to. p1 will appear to point to valid
memory; there's no good way to detect that this is merely accidental.
Tricks like writing 0xDEADBEEF into uninitialized memory can catch
some problems, but they can't catch everything.
--
Keith Thompson (The_Other_Keith) kst-u@xxxxxxx <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
.
- References:
- Detecting freed memory
- From: Rob
- Re: Detecting freed memory
- From: EventHelix.com
- Detecting freed memory
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