[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Old Index]
Re: toolchain/43234: lint warns about perfectly good casts
The following reply was made to PR toolchain/43234; it has been noted by GNATS.
From: David Holland <dholland-bugs%netbsd.org@localhost>
Subject: Re: toolchain/43234: lint warns about perfectly good casts
Date: Thu, 6 May 2010 08:22:38 +0000
On Tue, May 04, 2010 at 02:10:07PM +0000, Wolfgang Solfrank wrote:
> > foo.c(12): warning: pointer casts may be troublesome 
> Well, actually lint is perfectly correct in pointing out possible
> trouble here.
> I once worked on a 16 bit machine, where most addresses are
> 16 bit and point to 16 bit values, i.e., the machine has
> 65536 16 bit words or 128 kB of memory. In contrast to that,
> byte pointers are also 16 bits, but address bytes, i.e. the
> machine can only address the low 64 kB using character pointers.
> Casting an int pointer to a character pointer shifts the 16 bits
> one bit to the left, loosing the high bit (which poses trouble
> if the original value was in the upper 64 kB.) Of course the
> opposite cast shifts to the right, but you can't get the lost
> bit back.
Ouch. That isn't compatible with the C standard though. I don't think
lint should be worrying about such platforms... or at least not until
we find one we decide we want to port to, and when/if we do that lint
needs to be very specific about what it thinks might go wrong.
> I've got no idea, why lint doesn't warn if you add the extra
> cast through a void pointer.
Because it does purely local checks, i.e., it's dumb.
David A. Holland
Main Index |
Thread Index |