linux-kernel - Re: Why is the kfree() argument const?

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Date:	Thu, 17 Jan 2008 00:13:04 +0100
From:	Johannes Weiner <hannes@...urebad.de>
To:	Christoph Lameter <clameter@....com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	penberg@...helsinki.fi
Subject: Re: Why is the kfree() argument const?

Hi,

Christoph Lameter <clameter@....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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