From: Dave Dodge <dododge@dododge.net>
To: linux-hotplug@vger.kernel.org
Subject: Re: Segfault fix in scsi_id-0.6
Date: Wed, 29 Sep 2004 18:58:04 +0000 [thread overview]
Message-ID: <20040929190347.GA28198@basmati> (raw)
In-Reply-To: <20040929004539.GA2282@beaverton.ibm.com>
On Tue, Sep 28, 2004 at 05:45:39PM -0700, Patrick Mansfield wrote:
> On Tue, Sep 28, 2004 at 03:33:59PM -0600, Andrew Patterson wrote:
> > + serial = (char*) (((unaligned_buf - (char *)0) + (ALIGN - 1)) &
> > ~(ALIGN - 1));
Quick comment: the C compiler will treat the (char*)0 as a null
pointer constant. C makes no guarantee that the resulting value will
have anything to do with address 0. I believe there are architectures
where a null pointer has all-bits-on or some other non-zero
representation, though I don't know if Linux has ever been made to run
on any of them.
> But how about just casting to unsigned long instead? Like:
> + serial = (char*) (((unsigned long) unaligned_buf + (ALIGN - 1))
> + & ~(ALIGN - 1));
None of this pointer manipulation is technically defined to work, but
from a practical standpoint this will probably be safe. There's still
the possibility that an unsigned long can't hold all pointer values.
If you're willing to rely on a C99 construct, you could include
<stdint.h> and use uintptr_t instead.
-Dave Dodge
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next prev parent reply other threads:[~2004-09-29 18:58 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-09-29 0:45 Segfault fix in scsi_id-0.6 Patrick Mansfield
2004-09-29 18:58 ` Dave Dodge [this message]
2004-09-29 20:21 ` Andrew Patterson
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