linux-kernel - Re: [PATCH] ALSA: compress: Fix the mismatch size of struc between share lib(32bit) and kernel(64bit)

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Message-Id: <201406171348.59329.arnd@arndb.de>
Date:	Tue, 17 Jun 2014 13:48:59 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Vinod Koul <vinod.koul@...el.com>
Cc:	Takashi Iwai <tiwai@...e.de>,
	"Wang, Xiaoming" <xiaoming.wang@...el.com>, jeeja.kp@...el.com,
	dhowells@...hat.com, tglx@...utronix.de, mtk.manpages@...il.com,
	paulmck@...ux.vnet.ibm.com, davej@...hat.com,
	linux-kernel@...r.kernel.org, dongxing.zhang@...el.com
Subject: Re: [PATCH] ALSA: compress: Fix the mismatch size of struc between share lib(32bit) and kernel(64bit)

On Tuesday 17 June 2014, Vinod Koul wrote:
> > Anyway, if you use the __packed attribute, best apply it only to
> > the individual __u64 member(s), not the entire struct, otherwise
> > you might change user space programs in a subtle way when the alignment
> > changes from 4 to 1 byte. 
>
> then wouldn't it make sense to call out the aligned as well to ensure that it is
> aligning to what we want. Then we should add aligned (4) everywhere as mostly we
> need 4 byte aligned here

If you want to be explicit, then just mark the entire structure as
attribute((packed,aligned(4))), not each individual member.

	Arnd
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