linux-kernel - Re: [PATCH 16/16] fix handling of integer constant expressions

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Message-ID: <20070624214253.GL7590@daikokuya.co.uk>
Date:	Mon, 25 Jun 2007 06:42:53 +0900
From:	Neil Booth <neil@...kokuya.co.uk>
To:	Al Viro <viro@....linux.org.uk>
Cc:	Segher Boessenkool <segher@...nel.crashing.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-sparse@...r.kernel.org
Subject: Re: [PATCH 16/16] fix handling of integer constant expressions

Al Viro wrote:-

> > See gcc.gnu.org/PR456 for more discussion.  Yes it's an old
> > bug...
> 
> Humm...  Right, so __builtin_offsetof() needs special treatment too.
> Oh, bugger.  Is
> 	offsetof(struct foo, a.x[n])
> a documented extension?  I _know_ that it's not promised by 7.17,
> but gcc eats it (and obviously that sucker requires extra treatment
> in that case).

I asked on comp.std.c about this; the feeling was that only identifiers
are intended to be permitted as the 2nd argument to offsetof.  If true
the standard has a very obscure way of stating something that could
be said much more simply.

> Parsing __builtin_offsetof() arguments is going to be fun ;-/  Right
> now sparse has it as a predefined macro, but if we want to do that
> kind of analysis, we need to really parse it.  OTOH, that's not
> such a big deal...  Parser would need to accept
> 	ident ( \[ expr \] | . ident )*

don't forget -> if you're going to accept extra stuff.  GCC forgot ->
with the parser rewrite, yes I filed a PR.

Neil.
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