linux-kernel - Re: [PATCH] netlink: fix gcc -Wconversion compilation warning

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Message-Id: <20101217.120234.59681524.davem@davemloft.net>
Date:	Fri, 17 Dec 2010 12:02:34 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	ebiederm@...ssion.com
Cc:	kirill@...temov.name, netdev@...r.kernel.org, pablo@...filter.org,
	ldv@...linux.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] netlink: fix gcc -Wconversion compilation warning

From: ebiederm@...ssion.com (Eric W. Biederman)
Date: Mon, 13 Dec 2010 13:35:25 -0800

> "Kirill A. Shutsemov" <kirill@...temov.name> writes:
> 
>> From: Dmitry V. Levin <ldv@...linux.org>
>>
>> $ cat << EOF | gcc -Wconversion -xc -S -o/dev/null -
>> unsigned f(void) {return NLMSG_HDRLEN;}
>> EOF
>> <stdin>: In function 'f':
>> <stdin>:3:26: warning: negative integer implicitly converted to unsigned type
>>
> This doesn't look like a bad fix, but I believe things will fail if
> we give NLMSG_ALIGN an unsigned long like size_t.  Say like sizeof.

What are you talking about? That's exactly his test case,
look at what NLMSG_HDRLEN is defined to, it's exactly the
case you're worried "will fail", it passes sizeof() to
NLMSG_ALIGN.

I think I'll apply Kirill's original patch, it's good enough
and simpler.
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