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From: Joseph Myers <josmyers@redhat.com>
To: Qing Zhao <qing.zhao@oracle.com>
Cc: richard.guenther@gmail.com, uecker@tugraz.at,
	siddhesh@gotplt.org,  keescook@chromium.org,
	gcc-patches@gcc.gnu.org
Subject: Re: [RFC][PATCH v1 1/4] Documentation change
Date: Tue, 23 Apr 2024 18:04:22 +0000 (UTC)	[thread overview]
Message-ID: <74e0a96c-fa13-7fae-85e1-6e9efb28f4e@redhat.com> (raw)
In-Reply-To: <20240419184317.2138890-2-qing.zhao@oracle.com>

On Fri, 19 Apr 2024, Qing Zhao wrote:

> +The size of the union is as if the flexiable array member were omitted
> +except that it may have more trailing padding than the omission would imply.

"trailing padding" is more a concept for structures than for unions (where 
padding depends on which union member is active).  But I suppose it's 
still true that the union can be larger than without the flexible member, 
because of alignment considerations.

union u { char c; int a[]; };

needs to be sufficiently aligned for int, which means the size is a 
multiple of the size of int, whereas if the flexible array member weren't 
present, the size could be 1 byte.

-- 
Joseph S. Myers
josmyers@redhat.com


  parent reply	other threads:[~2024-04-23 18:05 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-04-19 18:43 [RFC][PATCH v1 0/4] Allow flexible array members in unions and alone in structures [PR53548] Qing Zhao
2024-04-19 18:43 ` [RFC][PATCH v1 1/4] Documentation change Qing Zhao
2024-04-19 20:54   ` Tom Tromey
2024-04-22 13:28     ` Qing Zhao
2024-04-23 18:04   ` Joseph Myers [this message]
2024-04-23 18:21     ` Qing Zhao
2024-04-23 19:03       ` Joseph Myers
2024-04-23 19:21         ` Qing Zhao
2024-04-19 18:43 ` [RFC][PATCH v1 2/4] C and C++ FE changes to support flexible array members in unions and alone in structures Qing Zhao
2024-04-23 19:51   ` Joseph Myers
2024-04-23 19:58     ` Qing Zhao
2024-04-19 18:43 ` [RFC][PATCH v1 3/4] Add testing cases for " Qing Zhao
2024-04-23 18:53   ` Joseph Myers
2024-04-23 19:30     ` Qing Zhao
2024-04-19 18:43 ` [RFC][PATCH v1 4/4] Adjust testcases for flexible array member in union and alone in structure extension Qing Zhao
2024-04-19 21:55 ` [RFC][PATCH v1 0/4] Allow flexible array members in unions and alone in structures [PR53548] Kees Cook

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