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Re: [Xen-devel] Should we revert "mm: New XENMEM space, XENMAPSPACE_gmfn_range"?



On 02/08/12 10:23, Jan Beulich wrote:
On 01.08.12 at 19:55, Stefano Stabellini<stefano.stabellini@xxxxxxxxxxxxx>  
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


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