From mboxrd@z Thu Jan  1 00:00:00 1970
From: Attilio Rao <attilio.rao@citrix.com>
Subject: Re: Should we revert "mm: New XENMEM space,
	XENMAPSPACE_gmfn_range"?
Date: Thu, 2 Aug 2012 10:45:13 +0100
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To: Jan Beulich <JBeulich@suse.com>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>, "Keir (Xen.org)" <keir@xen.org>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, "Tim (Xen.org)" <tim@xen.org>, Stefano Stabellini <Stefano.Stabellini@eu.citrix.com>, "allen.m.kay@intel.com" <allen.m.kay@intel.com>, Jean Guyader <jean.guyader@eu.citrix.com>, "Jean Guyader (3P)" <jean.guyader@citrix.com>
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On 02/08/12 10:23, Jan Beulich wrote:
>>>> On 01.08.12 at 19:55, Stefano Stabellini<stefano.stabellini@eu.citrix.com>  wrote:
>>>>          
>> I was reading more about this commit because this patch breaks the ABI
>> on ARM, when I realized that on x86 there is no standard that specifies
>> the alignment of fields in a struct.
>>      
> There is - the psABI supplements to the SVR4 ABI.
>
>    

This is a completely different issue.
The problem here gcc/whatever compiler padding added to the struct in 
order to have alignment of the members to the word boundry. The 
difference is that this is not enforced in the ARM case (apparently, 
from Stefano's report) while it happens in the x86 case.

This is why it is a good rule to organize member of a struct from the 
bigger to the smaller when compiling with gcc and this is not the case 
of the struct in question.

In the end it is a compiler decisional thing, not something decided by 
the ABI.

Attilio