linux-kernel - Re: [PATCH 2.6.17-rc6 7/9] Remove some of the kmemleak false positives

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Message-ID: <20060803063230.GY32572@devserv.devel.redhat.com>
Date:	Thu, 3 Aug 2006 02:32:30 -0400
From:	Jakub Jelinek <jakub@...hat.com>
To:	Catalin Marinas <catalin.marinas@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH 2.6.17-rc6 7/9] Remove some of the kmemleak false positives

On Mon, Jul 24, 2006 at 02:28:03PM +0100, Catalin Marinas wrote:
> On 24/07/06, Ingo Molnar <mingo@...e.hu> wrote:
> >update: there's also a neat gcc extension trick suggested by Arjan:
> >__builtin_classify_type(). This converts types into integers!
> 
> It's not really reliable as it doesn't distinguish well between types.
> All the structures, no matter what they contain, have the same id
> (which I think only refers to the fact that it is built-in type,
> pointer or structure, without differentiation).

__builtin_classify_type () doesn't give types unique ID, it only classifies
them:

/* Values returned by __builtin_classify_type.  */

enum type_class
{
  no_type_class = -1,
  void_type_class, integer_type_class, char_type_class,
  enumeral_type_class, boolean_type_class,
  pointer_type_class, reference_type_class, offset_type_class,
  real_type_class, complex_type_class,
  function_type_class, method_type_class,
  record_type_class, union_type_class,
  array_type_class, string_type_class,
  lang_type_class
};

All structures are given record_type_class, all unions union_type_class,
all pointers pointer_type_class, etc.
That doesn't mean you can't use it in the kernel as additional source
of type checking (in addition to e.g. sizeof and __alignof__).

	Jakub
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