[OE-core] Kernel: Builds use old version of defconfig

[Mike Looijmans]

On 24-11-16 11:10, Mike Looijmans wrote:
> I'm currently experiencing a problem with "defconfig" files and the kernel.
>
> In short, when I make a change to the "defconfig" file, the kernel is rebuilt
> (which is correct), but the resulting kernel has been built using the old
> defconfig from a previous build, instead of the new one.
>
> The kernel recipe just contains "file://defconfig" in its SRC_URI. The
> defconfig file is in the project's overlay.
>
> For example, I have a kernel with "CONFIG_DEVMEM" disabled:
>
> # gunzip < /proc/config.gz | grep DEVMEM
> # CONFIG_DEVMEM is not set
>
> Now, I change the defconfig to contain CONFIG_DEVMEM=y and build the image.
> The result:
>
> # gunzip < /proc/config.gz | grep DEVMEM
> # CONFIG_DEVMEM is not set
>
> So the change did not make it into the actual kernel, even though the kernel
> was rebuild as a result of the change.
>
> I run "bitbake -c cleansstate virtual/kernel" and build the image again:
>
> # gunzip < /proc/config.gz | grep DEVMEM
> CONFIG_DEVMEM=y
>
> After cleaning, the result is correct and the new defconfig is active.
>
> I'm trying to figure out how this can happen, any help is welcome...

What seems to be the problem is this code in kernel.bbclass:

	# Copy defconfig to .config if .config does not exist. This allows
	# recipes to manage the .config themselves in do_configure_prepend().
	if [ -f "${WORKDIR}/defconfig" ] && [ ! -f "${B}/.config" ]; then
		cp "${WORKDIR}/defconfig" "${B}/.config"
	fi

This keeps any existing ".config" file if it happens to still be in the $B 
path, which is the case if you're rebuilding a kernel.

I see two possible ways to fix this.

1) During "cleanup" also remove the .config file in the build dir. However, 
the build dir is probably kept alive for a reason? I also can't figure out how 
that "cleanup" is being done.


2) Remove the second part of the "if" statement, so it becomes:

	# Copy defconfig to .config if "defconfig" exists. This allows
	# recipes to manage the .config themselves in do_configure_prepend().
	if [ -f "${WORKDIR}/defconfig" ]; then
		cp "${WORKDIR}/defconfig" "${B}/.config"
	fi

I've tested that, and it solves my problem. However, it will probably break 
other people's config mangling?


Kind regards,

Mike Looijmans
System Expert

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