From: Johannes Weiner <hannes@saeurebad.de>
To: Christoph Lameter <clameter@sgi.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       penberg@cs.helsinki.fi
Subject: Re: Why is the kfree() argument const?
References: <87lk6pvii0.fsf@saeurebad.de>
	<alpine.LFD.1.00.0801161026550.2806@woody.linux-foundation.org>
	<87odblct19.fsf@saeurebad.de>
	<Pine.LNX.4.64.0801161419290.11922@schroedinger.engr.sgi.com>
Date: Thu, 17 Jan 2008 00:13:04 +0100
In-Reply-To: <Pine.LNX.4.64.0801161419290.11922@schroedinger.engr.sgi.com>
	(Christoph Lameter's message of "Wed, 16 Jan 2008 14:20:50 -0800
	(PST)")
Message-ID: <87bq7lcqke.fsf@saeurebad.de>
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Hi,

Christoph Lameter <clameter@sgi.com> writes:

> On Wed, 16 Jan 2008, Johannes Weiner wrote:
>
>> So if I got it right and you actually modify the memory you only got a
>> const pointer to, you reach a level where you _have to_ break this
>> policy and cast to a non-const pointer, as it is currently done in
>> kfree().  No?
>
> Correct and we have gcc 4.2 currently spitting out warnings because of 
> casting to non const. Any idea how to convince gcc that this is okay?

Just for the record, this really seems to be a gcc bug, I can not
explain this otherwise:

$ cat test.c
#include <stdio.h>

static void test(void *p)
{
        char *v = p;
        puts(v);
}

int main(void)
{
        const char foo[] = "foo";
        test((void *)foo);
        return 0;
}
$ gcc -Wall test.c -o test
$ gcc -Wall -O test.c -o test
test.c: In function 'main':
test.c:12: warning: passing argument 1 of 'test' discards qualifiers from pointer target type
$ gcc -Wall -O -fno-inline test.c -o test
$

gcc is version 4.2.2.

	Hannes
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