Malloc bug?

[Nathan Ingersoll]

According to what others have said, my program is probably overwriting a
buffer, or incorrectly freeing some variable, thus corrupting mallocs data
structures and causing a crash. So malloc works the way the man page
states, just not when its been corrupted.

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|   Nathan Ingersoll             |   Computer Science/Mathematics         |
|   mailto: ningerso at d.umn.edu   |   University of Minnesota-Duluth       |
|   http://umn.edu/~ningerso     |   http://www.d.umn.edu                 |
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On Wed, 19 Jul 2000, William Blew wrote:

> On Tue, 18 Jul 2000, David A. Gatwood wrote:
>
> Anybody know here man page patches are submitted? After all, if the
> man page is incorrect, an easy fix is to update it :).
>
> BTW: David, thanks for the info.
>
> > On Tue, 18 Jul 2000, Nathan Ingersoll wrote:
> >
> > > I've been working on a GTK program for a while now, and I've been
> > > experiencing segfaults within malloc. I was under the impression that
> > > malloc should always return successfully (at least that's what the man
> > > page says).
> >
> >
> > Sounds like the man page is wrong.  :-)  Malloc returns NULL if:
> >
> > 1.	the machine's virtual memory is exhausted
> > 2.	the process's maximum virtual memory (set by ulimit) is exhausted
> > 3.	the process's virtual memory has been hosed.
> >
> > There may be other cases, but I can't think of them, if there are.  The
> > first two are fairly trivial, and shouldn't happen unless you're
> > allocating in an infinite loop or something.
> >
> > There are four ways to get #3 that I can think of, probably more, but
> > these are the first ones that come to mind:
> >
> > a.	call free() on an unitialized pointer (containing random data).
> > b.	call free() twice on the same memory region.
> > c.	call free() on the middle of a malloc'ed region.
> > d.	call free() on a variable allocated by something other than
> > 	malloc, e.g. a stack variable (in a function or a function call),
> > 	a static variable (or any global variable), or a region allocated
> > 	by the C++ new function.
> >
> > Anyway, you should always check the return value of malloc.  :-)
> >
> >
> > > Any ideas what may be causing this? I don't know if this has
> > > anything to do with it, but the kernel I was using generated lots of
> > > vm_do_try_free_pages failed error logs but not necessarily during program
> > > execution.
> >
> > No idea about that.  The earlier points are machine-independent.  The
> > above looks like it's specific to the PPC monolithic kernel and/or GTK,
> > neither of which I do much with.
> >
> >
> > David
> >
> > ---------------------------------------------------------------------
> > A brief Haiku:
> >
> > Microsoft is bad.
> > It seems secure at first glance.
> > Then you read your mail.
> >
> >
> >
>
> --
> William Blew, wblew at home.com
> Gamer by Choice, Geek by Birth
>


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