From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Hurley <peter@hurleysoftware.com>
Subject: Re: bitfield structures
Date: Thu, 16 Oct 2014 11:57:18 -0400
Message-ID: <543FEADE.1010407@hurleysoftware.com>
References: <CADnq5_MNf4L2eqe0xA7dwLMj=4zfL3UsO_H9cvJMQfz93FUOeA@mail.gmail.com>
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To: Alex Deucher <alexdeucher@gmail.com>, Maling list - DRI developers <dri-devel@lists.freedesktop.org>
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On 10/16/2014 10:14 AM, Alex Deucher wrote:
> Are there any strong objections to these sorts of structures?

You may want to blacklist certain compiler version/arch combinations,
or get the affected arches to do it.

gcc up to 4.7.1 on ia64 and ppc64 generates 64-bit wide RMW cycles
on bitfields, regardless of the specified type or actual field width.
The enlarged write overwrites adjacent fields.

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52080

Regards,
Peter Hurley