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Re: [PATCH] inttostr.h: add compile-time buffer overrun checks

From: Pádraig Brady
Subject: Re: [PATCH] inttostr.h: add compile-time buffer overrun checks
Date: Tue, 19 Oct 2010 00:17:28 +0100
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20100227 Thunderbird/3.0.3

On 18/10/10 18:29, Paul Eggert wrote:
> On 10/18/10 04:53, Pádraig Brady wrote:
>> /* Like sizeof, except that it treats a variable sized array
>>    as a pointer rather than determining the size at runtime.  */
>> #define CT_SIZEOF(x) (__builtin_constant_p(sizeof x) ? sizeof x: sizeof 
>> (void*))
> I don't see how this would work.  If x is a variable-sized
> array, CT_SIZEOF(x) is not a constant expression, according
> to the C rules, because for A?B:C to be a constant expression,
> B and C both have to be constant expressions.

I did verify it, but on gcc 4.1.3.
I've just now checked that gcc 3.0 does also constant fold the above,
while gcc 2.95 does not.

> Besides, there's really not that much need to be worried about
> older GCC compilers.  They are being upgraded all the time, and
> the problem will go away.  In the meantime, we're going to be
> catching the errors anyway, since we'll be using the newer compilers.

I understand that. My main reasoning was to have
the simpler solution as a stepping stone to understanding
the more complicated one.


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