[oe] RFC: Adding a new global MACHINE_ENDIAN variable

[Koen Kooi]

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Rod Whitby schreef:
> Koen Kooi wrote:
>> Rod Whitby schreef:
>>>> There exist machines (like the ixp4xx range of processors) which can be
>>>> run in either little-endian or big-endian mode, and both modes are
>>>> supported by OE.
>>>>
>>>> I propose a new "MACHINE_ENDIAN" (naming courtesy of RP) variable to do
>>>> this selection (i.e. for machines that support both, the build can be
>>>> selected in local.conf).
>> No, that's just needles confusion, just make a .inc file (like ixp4xx.inc) that has the
>> common bits and 2 machine files that set up the appropriate endiannes stuff. That way you
>> can use machine overrides to configure stuff instead of putting more anonymous python
>> functions in the metadata.
> 
> There currently is an ARCH_BYTE_SEX "magic" variable (which nslu2-linux
> added), which is used 77 times in OE as it stands today (mostly in
> SlugOS files).  First thing I will do is replace that with
> MACHINE_ENDIAN (as it's a better name).
> 
> As for MACHINE_ENDIAN as a magic variable, to do as you suggest requires
> that there be an easy way to have a "machine architecture" override
> (i.e. ixp4xx) as well as the usual "actual machine/board" override (i.e.
> nslu2le).  Currently there is only one such override in place, which
> means that in *every* place that there currently is an _ixp4xx override
> in the metadata, that needs to have 2 other duplicates of that line (one
> for _nslu2le and one for _nslu2be) added in each of those .bb files.
> 
> I'm happy to go down that path instead of the MACHINE_ENDIAN path (if
> that's the consensus of all the OE core team members - RP and koen
> currently have diametrically opposed opinions on this - what do others
> think?).  But I will need a way of inserting "ixp4xxle/be" and "ixp4xx"
> in the set of overrides for both nslu2le and nslu2be machines.  I expect
> this will need to be done in the ixp4xx.conf file by some hacky python
> which looks for ${MACHINE} in the override list and adds "ixp4xxle/be"
> and "ixp4xx" after it.
> 
> Koen, with that extra information and context, is your input to the
> consensus still the same?

I think adding two machines adheres to the principle of least surprise and makes is
possible to build for the 2 machines in parallel (/me hugs bitbake trunk + machine-via-env).
Also take a look at the amount of python in ixp4xx.conf to translate endianness into
various settings. With 2 machines, you can do without the python, which makes it for new
OE users look less arcane, and easier for python n00bs like me to modify.

regards,

Koen


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