Re: toolchain/43234: lint warns about perfectly good casts

[Wolfgang Solfrank <Wolfgang%Solfrank.net@localhost>]

The following reply was made to PR toolchain/43234; it has been noted by GNATS.

From: Wolfgang Solfrank <Wolfgang%Solfrank.net@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: toolchain/43234: lint warns about perfectly good casts
Date: Tue, 04 May 2010 16:09:52 +0200

 Hi,
 
 > Use lint -chapbxzFS per sys.mk. It says
 >
 > foo.c(12): warning: pointer casts may be troublesome [247]
 
 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.
 
 I've got no idea, why lint doesn't warn if you add the extra
 cast through a void pointer.
 
 Ciao,
 Wolfgang
 -- 
 Wolfgang%Solfrank.net@localhost                                Wolfgang 
Solfrank