linux-kernel - Re: [RFC PATCH] type safe allocator

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Message-ID: <20070802120515.GL21089@ftp.linux.org.uk>
Date:	Thu, 2 Aug 2007 13:05:15 +0100
From:	Al Viro <viro@....linux.org.uk>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, akpm@...ux-foundation.org
Subject: Re: [RFC PATCH] type safe allocator

On Thu, Aug 02, 2007 at 09:27:57AM +0200, Miklos Szeredi wrote:
> > Quite frankly, I suspect you would be better off just instrumenting 
> > "sparse" instead, and matching up the size of the allocation with the type 
> > it gets assigned to.
> 
> But that just can't be done, because kmalloc() doesn't tell us the
> _intent_ of the allocation.

Of course it can be done.  When argument has form sizeof(...), attach
the information about target of pointer to the resulting void *; have
? : between pointer to object and that one warn if types do not match,
? : between void * and that one lose that information, ? : between
two such warn when types do not match.  On assigment-type operations
(assignment, passing argument to function, initializer, return) when
the type of target is pointer to object (and not void *) warn if
types do not match.  Have typeof lose that information.

Not even hard to implement; just let us finish cleaning the lazy examination
logics up first (~5-6 patches away).

FWIW, I object against the original proposal, no matter how you name it.
Reason: we are introducing more magical constructs that have to be known
to human reader in order to parse the damn code.

Folks, this is serious.  _We_ might be used to having in effect a C dialect
with extensions implemented by preprocessor.  That's fine, but for a fresh
reader it becomes a problem; sure, they can dig in include/linux/*.h and
to some extent they clearly have to.  However, it doesn't come for free
and we really ought to keep that in mind - amount of local idioms (and
anything that doesn't look like a normal function call with normal arguments
_does_ become an idiom to be learnt before one can fluently RTFS) is a thing
to watch out for.

IOW, whenever we add to that pile we ought to look hard at whether it's worth
the trouble.
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