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Re: memset (0, 0, 0);
- From: Richard Earnshaw <rearnsha at arm dot com>
- To: Daniel Jacobowitz <drow at mvista dot com>
- Cc: Richard dot Earnshaw at arm dot com, "Thomas, Stephen" <stephen dot thomas at superh dot com>, Geoff Keating <geoffk at geoffk dot org>, gdb at sources dot redhat dot com, newlib at sources dot redhat dot com, bug-glibc at gnu dot org, "McGoogan, Sean" <sean dot mcgoogan at superh dot com>, Andrew Cagney <ac131313 at redhat dot com>
- Date: Tue, 08 Apr 2003 14:45:11 +0100
- Subject: Re: memset (0, 0, 0);
- Organization: ARM Ltd.
- Reply-to: Richard dot Earnshaw at arm dot com
> On Tue, Apr 08, 2003 at 10:29:55AM +0100, Richard Earnshaw wrote:
> > >
> > > Hi Geoff,
> > >
> > > Which xmalloc are you referring to? The xmalloc in this case is a gdb internal function, defined in gdb/utils.c:
> > >
> > > PTR xmalloc (size_t size)
> > > {
> > > return xmmalloc (NULL, size);
> > > }
> > >
> > > And xmmalloc is:
> > >
> > > void * xmmalloc (void *md, size_t size)
> > > {
> > > void *val;
> > >
> > > if (size == 0)
> > > {
> > > val = NULL;
> > > }
> > > else
> > > {
> > > val = mmalloc (md, size);
> > > if (val == NULL)
> > > nomem (size);
> > > }
> > > return (val);
> > > }
> > >
> > > So size=0 does indeed return NULL. Also, I have single stepped this code to verify that this is actually what happens.
> >
> > It looks as though that implementation of xmalloc doesn't match the
> > general specification of xmalloc, which is that xmalloc must *never*
> > return NULL (see libiberty/xmalloc.c for the specification).
> >
> > I'm not sure why gdb is trying to provide its own implementation of these
> > functions and not use those in libiberty. Andrew?
>
> The ones in libiberty call exit; the ones in gdb call error() and
> unwind cleanups. GDB prefers not to abort when it runs out of memory,
> esp. if it can just abort the current operation and reclaim memory.
>
That's ok, but the bit about returning NULL isn't. If we want a "malloc"
routine that always returns NULL on zero size, we shouldn't call it
xmalloc.
R.