[linux-yocto] where are the tunes in TUNE_FEATURES defined

[Cristian Bercaru]

Hello!

I see that each poky build has a variable named TUNE_FEATURES, that 
looks like this
     TUNE_FEATURES = "m32 fpu-hard ppc476"

Where in poky are "m32", "fpu-hard", "ppc476" etc defined?

I'm interested in compiling a 32-bit linux kernel and root file system 
for an armv8 cpu.

If possible, I also want to instruct gcc to make optimizations for 
cortex-a53 [1] and cortex-a57 [2] so I want to find the definitions of 
these TUNE_FEATURES and see what other optimizations I can add to my build.

[1] http://www.arm.com/products/processors/cortex-a/cortex-a53-processor.php
[2] http://www.arm.com/products/processors/cortex-a/cortex-a57-processor.php

Thank you,
Cristian Bercaru