linux-kernel - Re: somebody dropped a (warning) bomb

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Date:	Mon, 12 Feb 2007 14:12:28 +0300
From:	Sergei Organov <osv@...ad.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"J.A. MagallÃÂ³n" <jamagallon@....com>,
	Jan Engelhardt <jengelh@...ux01.gwdg.de>,
	Jeff Garzik <jeff@...zik.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: somebody dropped a (warning) bomb

Linus Torvalds <torvalds@...ux-foundation.org> writes:
> On Fri, 9 Feb 2007, Sergei Organov wrote:
>> 
>> As far as I can read the C99 standard, the "char", "signed char", and
>> "unsigned char", are all different types:
>
> Indeed. Search for "pseudo-unsigned", and you'll see more. There are 
> actually cases where "char" can act differently from _both_ "unsigned 
> char" and "signed char".
>
>> If so, then the code above is broken no matter what representation of
>> "char" is chosen for given arch, as strcmp() takes "char*" arguments,
>> that are not compatible with either "signed char*" or "unsigned char*".
>
> ..and my argument is that a warning which doesn't allow you to call 
> "strlen()" on a "unsigned char" array without triggering is a bogus 
> warning, and must be removed.

Why strlen() should be allowed to be called with an incompatible pointer
type? My point is that gcc should issue *different warning*, -- the same
warning it issues here:

$ cat incompat.c
void foo(int *p);
void boo(long *p) { foo(p); }
$ gcc -W -Wall -c incompat.c
incompat.c:2: warning: passing argument 1 of 'foo' from incompatible pointer type

Calling strlen(char*) with "unsigned char*" argument does pass argument
of incompatible pointer type due to the fact that in C "char" and
"unsigned char" are two incompatible types, and it has nothing to do
with signedness.

[...]

-- Sergei.
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