If you set SDKMACHINE in the distro config it will not have any effect; this is because of the ordering in meta/conf/bitbake.conf: ... include conf/machine-sdk/${SDKMACHINE}.conf include conf/distro/${DISTRO}.conf ... The value won't get set until after the line where its value would have any effect has been parsed. Assuming we can't reorder the includes in bitbake.conf, I think we should add a check in sanity.bbclass to see if the include actually happened assuming SDKMACHINE has a value. This should be a simple matter of checking BBINCLUDED.
Added a check in sanity.bbclass to determine if the SDKMACHINE value has really taken effect; this has now been merged: http://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?id=49f2bc450c1dd969eba30287050e25030116b714 We need to note in the manual that SDKMACHINE cannot be set in the distro config.
See http://www.yoctoproject.org/docs/1.6/ref-manual/ref-manual.html#var-SDKMACHINE for the note that takes care of this doc part. I have run the changes by Paul and he approved them. Setting the documentation flag to "Done." Scott