[OE-core] [PATCH 2/2] kernel: check for empty .config file after merge_config.sh

[Flavio Suligoi]

Hi Bruce,

> Sometimes, for example in case of missed dependecies, after the
> execution of:
> 
> merge_config.sh
> 
> the resulting file ".config" can be empty.
> This is the reason why is necessary test it and, in case, display
> the "Could not configure ..." error message.
> 
> This doesn't belong here. Auditing of the final .config is done in a separate task, and we could pickup that issue there.
> 
> That being said, there are already checks for inputs that could result in something like this. How were you triggering this issue ? I'd like to reproduce it here, and perhaps come up with a different solution.
> 
> Bruce

I encountered this problem of the empty .config when I integrated 
the kernel 4.19 in my custom meta-layer based on a poky "rocko" (2.4) version.

The kernel 4.19 requires the following dependencies in the kernel recipe:

do_kernel_configme[depends] += "virtual/${TARGET_PREFIX}binutils:do_populate_sysroot"
do_kernel_configme[depends] += "virtual/${TARGET_PREFIX}gcc:do_populate_sysroot"
do_kernel_configme[depends] += "bc-native:do_populate_sysroot bison-native:do_populate_sysroot"

(in the thud version of poky these dependencies are already integrated in the
kernel-yocto.bbclass, but not in rocko)

Without these dependencies the merge_config.sh fails without any error messages,
the distro build process proceeds, but the built kernel is completely wrong
(no modules and only default config).

For this reason I added the additional error log:

${meta_dir}/cfg/merge_config_build-errors.log

and the check for the empty .config

Flavio