malloc() behavior (was: Pointer please)

[James Jacobsen]

It does not matter what freebsd does, C does not require that malloc  
initialize space according to Kernighan and Ritchie. Its a good book, I  
would say its worth the forty dollars.

--Will


On 10/05/03 20:32:00, Dan Nelson wrote:
> In the last episode (Oct 05), Robert Huff said:
> > Dan Nelson writes:
> > >  Could be one of two problems.  The program either malloced  
> memory
> > >  and tried to use it without zeroing it, or it freed some memory
> > >  and tried to keep using it.  In -current, the malloc has the J
> > >  debugging flag set, which fills malloced and freed memory with
> > >  0xd0 (see the malloc manpage).
> >
> > 	On that page (on my 5.1 system), it says malloc() does not
> zero
> > allocated pages.  Is this a change (possibly just for CURRENT), and
> > if so since when?  Bexause unless I'm delusional (possible) I
> thought
> > pages /were/ supposed to be zeroed, and doing so was one of the
> > system's "as time permits" chores.
> 
> Pages handed to processes by the kernel are always zeroed, but pages
> free()d then malloc()ed again are not zeroed by default on -RELEASEs,
> because they usually aren't returned back to the kernel inbetween
> (unless H is set, and even then it's not guaranteed).  -CURRENT  
> always
> has the J flag set, which means that any memory returned by malloc or
> passed to free will get overwritten with 0xD0, to aid debugging.
> That's not mentioned in the manpage, although I think it is mentioned
> someplace else (either FAQ or handbook).
> 
> --
> 	Dan Nelson
> 	dnelson at allantgroup.com
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