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To: Peter Jeremy <peterjeremy@optushome.com.au>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Sat, 25 Mar 2006 19:10:38 +1100."
	<20060325081037.GC703@turion.vk2pj.dyndns.org> 
Date: Sat, 25 Mar 2006 09:19:23 +0100
Message-ID: <62921.1143274763@critter.freebsd.dk>
Sender: phk@critter.freebsd.dk
Cc: Jason Evans <jasone@freebsd.org>, freebsd-arch@freebsd.org
Subject: Re: Proposed addition of malloc_size_np() 
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In message <20060325081037.GC703@turion.vk2pj.dyndns.org>, Peter Jeremy writes:
>On Sat, 2006-Mar-25 08:46:36 +0100, Poul-Henning Kamp wrote:
>>In message <44247DF1.8000002@FreeBSD.org>, Jason Evans writes:
>>>=== Proposal ===
>>>Add malloc_size_np() to libc, and provide the prototype in malloc_np.h:
>>>
>>>	size_t
>>>	malloc_size_np(const void *ptr);
>>
>>I'm for the concept, but wonder if it would be smarter to make it
>>
>>	void *
>>	malloc_np(size_t, size_t *)
>>
>>so we can do it in one go ?
>
>That restricts its use to malloc() wrappers.  I can also see the
>benefit in a function trying to validate the size of an arbitrary
>piece of memory that has been passed to it.

No you can't, because you cannot be certain that the pointer passed
to you is actually an unadultered malloc pointer.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.