Re: [RFC][PATCH 3/5] ksm source code

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Chris Wright wrote:
>>>  struct ksm_memory_region {
>>>  	__u32 npages; /* number of pages to share */
>>>  	__u64 addr; /* the begining of the virtual address */
>>>  };
>>>       
>> why isnt it compat safe?
>>     
>
> 32-bit has more relaxed alignment requirement for __u64 (4 bytes)
> than 64-bit (8 bytes).  choices are reverse the order or add padding
> (can test by compiling structure in 32 and 64 bit).
>   

Reversing the order isn't good enough, since the structure size would be 
different, and that is embedded in the ioctl number.  Padding is necessary.

[wishlist: struct { ... } __attribute__((abi_x86_64));]

-- 
Any sufficiently difficult bug is indistinguishable from a feature.


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