linux-hardening - Re: [wish] Flexible array members in unions

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Message-ID: <bb3aac3c-f377-5598-cbf6-47d0be448f3@codesourcery.com>
Date:   Thu, 11 May 2023 21:43:49 +0000
From:   Joseph Myers <joseph@...esourcery.com>
To:     Kees Cook <keescook@...omium.org>
CC:     Alejandro Colomar <alx.manpages@...il.com>, GCC <gcc@....gnu.org>,
        Alejandro Colomar <alx@...nx.com>,
        Andrew Clayton <a.clayton@...nx.com>,
        Andrew Clayton <andrew@...ital-domain.net>,
        <linux-hardening@...r.kernel.org>
Subject: Re: [wish] Flexible array members in unions

On Thu, 11 May 2023, Kees Cook via Gcc wrote:

> Why are zero-sized objects missing in Standard C? Or, perhaps, the better
> question is: what's needed to support the idea of a zero-sized object?

Zero-sized objects break the principle that different objects have 
different addresses, and the principle of being able to subtract pointers 
to different elements of an array.  There would also be serious C++ 
compatibility concerns, since C++ allows a struct with no members but it 
has nonzero size, unlike the GNU C extension where a struct with no 
members has size zero.

-- 
Joseph S. Myers
joseph@...esourcery.com