[Buildroot] auto-detecting toolchain metadata?

[Thomas Petazzoni <thomas.petazzoni@free-electrons.com>]

Hello,

On Tue, 22 Nov 2016 08:12:34 -0800, Hollis Blanchard wrote:

> OK, how can I use defconfig fragments? I can't find mention of it in the 
> manual or the top-level Makefile.

Easy:

 cat frag1 frag2 frag3 > defconfig

And that's it. There's nothing fancy in fragments, it's just a fragment
of defconfig, and you create the real defconfig by concatenating
fragments.

> I do see a little information about using config fragments for 
> Kconfig-based packages, and that says it breaks savedefconfig. So if I 
> can use fragments for the BR defconfig, how could I update the defconfig 
> in the future?

Fragments are hand-written, by extracting data from a defconfig.
Typically, with the above example, you generate your defconfig from
frag1, frag2 and frag3. You then run "make menuconfig", which updates
your configuration, and run "make savedefconfig", which generates a new
defconfig.

It is impossible for Buildroot to know in which fragment should a given
change be propagated. So what I typically do is "diff -u defconfig.old
defconfig", and then propagate the change to the appropriate fragment.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com