[yocto] sstate cache not used when adding custom task

[Andreas Fenkart]

Hi,

A custom task in a bbclass causes all recipes including it to be
rebuilt every time. Link to full bbclass attached below.

I already stripped that task down to this


    addtask check after do_compile before do_build
    addons_do_check() {
        :
    }

If I remove the addtask line, the recipe is not rerun:

$ bitbake recipe_name
NOTE: Tasks Summary: Attempted 2746 tasks of which 2746 didn't need to
be rerun and all succeeded.

With the 'addtask check' all task of the recipe from fetch till
rm_work_all is executed every time.

>From the cooker log, do_populate_sysroot is the last task running
before do_build was, hence I changed the addtask line to this:
addtask check after do_populate_sysroot before do_build

Then the recipe will not start from do_fetch on rerun, but will
reuse the previous do_populate_sysroot run. Hence only the last 4
tasks are run (do_check, do_build, do_rm_work, do_rm_work_all)

I experimented with bitbake-diffsig/bitbake-dumpsig, but the hash
of the stamp files (do_check) are identical on each run, of
course its content too. Only the timestamp of the stamp file
changes each run.
I'm confused what triggers the rebuild. I looked into bitbake
trying to understand how the task dependency is calculated, how
the sstate files are used. But it's quite a biest and will take
me quite some time to understand.

Any hints or regarding the issue or simply where to put a print
in bitbake to get me started was welcome.

This is still yocto 2.0.2 as we missed a couple of upgrades.

The full bbclass with the do_check task
https://git.digitalstrom.org/dss-oe/dss-oe/blob/master/yocto/dS/meta-digitalstrom-devel/classes/addons.bbclass#L46

/Andreas