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To: dewar@gnat.com
Cc: Dautrevaux@microprocess.com, paulus@samba.org,
        Franz.Sirl-kernel@lauterbach.com, benh@kernel.crashing.org,
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Subject: Re: [PATCH] C undefined behavior fix
In-Reply-To: <20020103132837.71EFBF3257@nile.gnat.com>
From: Florian Weimer <fw@deneb.enyo.de>
Date: Fri, 04 Jan 2002 09:38:35 +0100
In-Reply-To: <20020103132837.71EFBF3257@nile.gnat.com> (dewar@gnat.com's
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dewar@gnat.com writes:

> <<No, in fact the kernel isn't written in ANSI C. :)
> If nothing else, the fact that it uses a lot of gcc-specific
> extensions rules that out.  And it assumes that you can freely cast
> pointers to unsigned longs and back again.  I'm sure others can add to
> this list.
>>>
>
> Most certainly this list should exist in precise defined form. 

C99 includes a list of additional guarantees made by many C
implementations (in an informative index).  I think we really should
check this list (and the list of implementation-defined behavior) and
document the choices made by GCC.  In fact, this documentation is
required by the standard.

> It is this kind of informality that is asking for trouble.

We have seen much trouble in this area before, but I doubt we can
avoid all of them by proper documentation.  Quite a few people seem to
write some C code, check that it works, look at the generated machine
code, and if it seems to be correct, the C code is considered to be
correct.
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