[Buildroot] auto-detecting toolchain metadata?

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

Hello,

On Mon, 21 Nov 2016 17:04:57 -0800, Hollis Blanchard wrote:

> > with that output to be used as a base defconfig, then that would be
> > tremendously useful, indeed.  
> My use case is slightly different; I already have a defconfig; I just 
> want this script to replace the toolchain-related bits of it. Would 
> editing defconfig "in place" (e.g. create .defconfig.new, copy it over 
> the original) be acceptable?

How are you going to filter out all the toolchain-related options from
the original defconfig? It's not like all of them are prefixed by
"BR2_TOOLCHAIN" for example. So I hardly see how you can achieve what
you want in a reliable way.

> > And probably not very dificult to do either...  
> Here's one complexity: once we know the version, which GCC_AT_LEAST_X_Y 
> should be emitted? (Probably the same question for the other "AT_LEAST" 
> variables too.)
> 
> We could make a new list that matches toolchain/toolchain-common.in, but 
> that will undoubtedly lead to mismatches in the future...
> 
> We could just auto generate every major/minor version from 4.0 up to 
> <toolchain version>, but then how many minors for each major? 10? That 
> would yield 4.0 -> 4.10, 5.0 -> 5.10, 6.0 -> 6.10, ...

For gcc versions >= 5, we don't have an option for each minor version.
So it's actually pretty easy:

 if major < 5:
   option = BR2_TOOLCHAIN_GCC_AT_LEAST_<major>_<minor>
 else
   option = BR2_TOOLCHAIN_GCC_AT_LEAST_<major>

Best regards,

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