fixed memory bytes

Rajat Sharma fs.rajat at
Wed Jan 5 01:13:16 EST 2011

A nice kernel document regarding unaligned memory access. It may not
be directly answering all the questions asked, but once gone through
and understood completely, it will become easy to figure out how to
write portable kernel code.


On Wed, Jan 5, 2011 at 4:29 AM, julie Sullivan <kernelmail.jms at> wrote:
>> i have seen many places in  kernel where the variables specially the
>> structures should be of  fixed size independent of the architecture. i went
>> through the  definitions of them  but dint  get  clearly (or frankly  say
>> ...dint get them even a bit) .
> Hi Mohit
> I'm not sure whether we are interpreting your question correctly. Do you
> mean
> 1. you've seen some code in the kernel which you think means the size of a
> structure/
> variable (and its resulting binary footprint) is set to be the same (in
> bytes),
> regardless of the architecture, and you are confused about it?
> 2. you think that there should be a way of fixing the structure/variable
> (binary footprint)
> size to be the same (in bytes) regardless of the architecture and you are
> wondering if this
> is possible?
> In my (uninformed) opinion (2) is not be possible with the kernel due to
> portability
> issues - not only do natural word types differ (as others here are
> explaining) but you
> have no control over what optimization settings the kernel's user might set
> in gcc,
> for example. This is one of the problems with trying to maintain
> closed-source drivers
> and other binary code for the kernel, as I understand.
> Thanks
> Julie
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