Re: sparse preprocessing confused

From: Josh Triplett <josh@freedesktop.org>
To: Chris Wedgwood <cw@f00f.org>
Cc: Neil Booth <neil@daikokuya.co.uk>,
	Morten Welinder <mwelinder@gmail.com>,
	Randy Dunlap <rdunlap@xenotime.net>,
	linux-sparse@vger.kernel.org
Subject: Re: sparse preprocessing confused
Date: Sat, 28 Apr 2007 23:36:18 -0700	[thread overview]
Message-ID: <46343CE2.80403@freedesktop.org> (raw)
In-Reply-To: <20070429054143.GA15365@tuatara.stupidest.org>

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Chris Wedgwood wrote:
> On Thu, Apr 26, 2007 at 11:38:52PM +0900, Neil Booth wrote:
>>>>        memcpy(data + nhead, skb->head,
>>>> #ifdef NET_SKBUFF_DATA_USES_OFFSET
>>>>                skb->tail);
>>>> #else
>>>>                skb->tail - skb->head);
>>>> #endif
>>> If memcpy happens to be a macro, that is not valid C.
>> It's undefined rather than invalid.  GCC makes an effort to
>> do "what you'd expect".
> 
> I think I prefer sparse breaking on things like this (so we can find
> such uglies and correct them.).

I tend to agree; however, if GCC accepts the code, I would prefer to have
Sparse parse it and warn, rather than failing to parse it.  I would gladly
take a clean patch that allows this code to work the same way GCC does.  Bonus
if the patch supplies a -Wpreprocessor-conditional-in-macro-arguments or
similar, and I wouldn't object to having such a warning on by default.

- Josh Triplett

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