From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chen Gang Subject: Re: [PATCH] drivers: staging: lustre: lustre: include: add "__attribute__((packed))" for the related union Date: Mon, 03 Feb 2014 19:35:24 +0800 Message-ID: <52EF7EFC.5040704@gmail.com> References: <20140118142404.GT7444@mwanda> <52DBA3D4.3090308@gmail.com> <52DD0EFF.2010305@imgtec.com> <20140120123045.GV7444@mwanda> <52DD18A5.1090308@imgtec.com> <20140120125603.GD4815@mwanda> <20140120211356.GG4815@mwanda> <52DE4DA3.7090301@imgtec.com> <52E3A642.7010307@gmail.com> <52ECFD53.7010401@gmail.com> <20140203085855.GA26722@mwanda> <52EF6965.6040406@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: James Hogan , devel-gWbeCf7V1WCQmaza687I9mD2FQJk+8+b@public.gmane.org, andreas.dilger-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, Antonio Quartulli , Greg KH , bergwolf-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , David Miller , oleg.drokin-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, jacques-charles.lafoucriere-KCE40YydGKI@public.gmane.org, jinshan.xiong-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, netdev , linux-metag-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, David Laight To: Dan Carpenter Return-path: In-Reply-To: <52EF6965.6040406-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Sender: linux-metag-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: netdev.vger.kernel.org On 02/03/2014 06:03 PM, Chen Gang wrote: > On 02/03/2014 04:58 PM, Dan Carpenter wrote: >> On Sat, Feb 01, 2014 at 09:57:39PM +0800, Chen Gang wrote: >>> It seems, our kernel still stick to treate 'pack' region have effect >>> with both 'align' and 'sizeof'. >>> >> >> It's not about packed regions. It's about unions. It's saying the >> sizeof() a union is a multiple of 4 unless it's packed. >> >> union foo { >> short x; >> short y; >> }; >> >> The author intended the sizeof(union foo) to be 2 but on metag arch then >> it is 4. >> > > Yeah, just like your original discussion. :-) > > > Hmm... can we say: "for metag compiler, in a pack region, it considers > variables alignment, but does not consider about struct/union alignment > (except append packed to each related struct/union)". > > For compatible (consider about its ABI), it has to keep this features, > but for kernel, it needs be changed. > > So, I suggest to add one parameter to compiler to switch this feature, > and append this parameter to KBUILD_CFLAGS in "arch/metag/Makefile" > which can satisfy both ABI and kernel. > After append the parameter to KBUILD_CFLAGS in "arch/metag/Makefile", - I guess/assume "include/uapi/*" should/will not need be modified. - but need check all files in "arch/metag/include/uapi/*". (add padding data for packed struct/union when __KERNEL__ defined) - maybe we have to process metag related ABI which not in "*/uapi/*" (add padding data for packed struct/union when __KERNEL__ defined) and when we find them, recommend to move all of them to "*/uapi/*". Sorry, I don't know whether this way is the best way or not, but for me it is an executable way to solve this feature issue and satisfy both kernel and ABI. Thanks. -- Chen Gang Open, share and attitude like air, water and life which God blessed -- To unsubscribe from this list: send the line "unsubscribe linux-metag" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html