linux-kernel - Re: [PATCH v2 6/7] staging: android: binder: fix alignment issues

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Message-ID: <CAMP5Xgew5_F2De2+7Ny39iww2Un6hC8B3aYNV7CEawovkFg1Og@mail.gmail.com>
Date:	Tue, 9 Apr 2013 16:58:56 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	Serban Constantinescu <serban.constantinescu@....com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	John Stultz <john.stultz@...aro.org>,
	Dave Butcher <Dave.Butcher@....com>
Subject: Re: [PATCH v2 6/7] staging: android: binder: fix alignment issues

On Tue, Apr 9, 2013 at 3:00 AM, Serban Constantinescu
<serban.constantinescu@....com> wrote:
> The Android userspace aligns the data written to the binder buffers to
> 4bytes. Thus for 32bit platforms or 64bit platforms running an 32bit
> Android userspace we can have a buffer looking like this:
>
> platform    buffer(binder_cmd   pointer)      size
> 32/32                 32b         32b          8B
> 64/32                 32b         64b          12B
> 64/64                 32b         64b          12B
>
> Thus the kernel needs to check that the buffer size is aligned to 4bytes
> not to (void *) that will be 8bytes on 64bit machines.
>
> The change does not affect existing 32bit ABI.
>

Do we not want the pointers to be 8 byte aligned on 64bit platforms?

--
Arve Hjønnevåg
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