[Buildroot] [PATCH 2/3 v3] linux: kconfig needs host-{flex, bison} to build the configurators

[Thomas Petazzoni <thomas.petazzoni@bootlin.com>]

Hello,

On Wed, 15 Aug 2018 00:50:42 +0200, Arnout Vandecappelle wrote:

>  My position is that we do indeed need our host flex and bison for everything
> installed in target/ (which implies everything installed in staging/), but not
> for things installed in host/. We definitely need it for BR2_REPRODUCIBLE.
> 
>  It would also be nice if dependencies.sh could do a version check and accept
> the system flex/bison if it is the right version, like we do for cmake and tar.
> 
>  But both of these wishes make things more complicated, so I'm OK with just
> keeping all current host-flex/bison dependencies.

In fact, I think adding flex and bison as mandatory dependencies of the
system is going to cause too much disruption. All the autobuilders
would start complaining, all the Travis/Gitlab CI setups would have to
be adjusted, and everyone building in containers/minimal environments
will be affected.

So instead, I'd like to detect if flex/bison are available on the
system. If they are available, then we use them for the Linux kernel
configuration process. If they are not available, we build them.

Instead of:

  LINUX_KCONFIG_DEPENDENCIES = host-bison host-flex

I'd prefer to see:

  LINUX_KCONFIG_DEPENDENCIES = $(BR2_FLEX_HOST_DEPENDENCY) $(BR2_BISON_HOST_DEPENDENCY)

And the usual logic in support/dependencies/ to check for bison/flex.
This will avoid disrupting all existing setups, and still provide the
speed-up that we don't need to build flex/bison when doing "make
linux-menuconfig".

> > For the linux kernel and other kconfig-based packages, we don't care
> > which flex/bison are used, because the resulting binaries are not
> > installed, unless those packages also generate code eventually installed
> > in host/, staging/ or target/  
> 
>  Note that this means you'll still need host-flex/bison for the kernel, because
> the kernel may build dtc and that gets installed in host...

Are you sure flex/bison are used when building the DTC copy in the
Linux kernel ? Indeed we only added host-bison/host-flex as
dependencies of linux in commit
1b9faedf32be26d9c983c573ccd98f57fc6f6569, when kconfig stopped shipping
its pre-generated files. How could DTC be built before
1b9faedf32be26d9c983c573ccd98f57fc6f6569 if it required bison/flex ?

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com