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Date: Mon, 03 Feb 2014 19:35:24 +0800 From: Chen Gang <gang.chen.5i5j@...il.com> To: Dan Carpenter <dan.carpenter@...cle.com> CC: James Hogan <james.hogan@...tec.com>, devel@...verdev.osuosl.org, andreas.dilger@...el.com, Antonio Quartulli <antonio@...hcoding.com>, Greg KH <gregkh@...uxfoundation.org>, bergwolf@...il.com, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, David Miller <davem@...emloft.net>, oleg.drokin@...el.com, jacques-charles.lafoucriere@....fr, jinshan.xiong@...el.com, netdev <netdev@...r.kernel.org>, linux-metag@...r.kernel.org, David Laight <David.Laight@...LAB.COM> Subject: Re: [PATCH] drivers: staging: lustre: lustre: include: add "__attribute__((packed))" for the related union 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 netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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