How does bitbake build kernel recipes?

Question

I am currently learning openBMC by analyzing the bitbake build process. I have encountered a question about how bitbake connects image recipes and kernel recipes.

Using IBM Romulus as an example: The PREFERRED_PROVIDER_virtual/kernel will be set "linux-aspeed" in the read configuration stage

Here is a simplified hierarchy of the configuration files:

conf/bitbake.conf
    /home/leo/Documents/openbmc/meta-ibm/meta-romulus/conf/machine/romulus.conf
        /home/leo/Documents/openbmc/meta-aspeed/conf/machine/include/ast2500.inc
            /home/leo/Documents/openbmc/meta/conf/machine/include/soc-family.inc
            /home/leo/Documents/openbmc/meta-aspeed/conf/machine/include/aspeed.inc

As far as I know, the purpose of PREFERRED_PROVIDER_virtual/kernel is to select a preferred kernel recipe when there are multiple providers. In the case of "linux-aspeed," the linux-aspeed.inc file indeed contains PROVIDES += "virtual/kernel".

However, these variables alone do not determine whether the build process should proceed directly.

When compiling with bitbake obmc-phosphor-image, the process goes through the following hierarchy:

obmc-phosphor-image.bb
    obmc-phosphor-image.bbclass
        core-image.bbclass
            image.bbclass

For installing other recipes, the common method is to pass the package or recipe name to the PACKAGE_INSTALL variable. However, there is no information in these files about using FEATURE_PACKAGES to record dependencies like DEPENDS or RDEPENDS:${PN} = "virtual/kernel".

Or specify the recipe directly via OBMC_IMAGE_EXTRA_INSTALL.

In image.bbclass, there are sections like:

    KERNELDEPMODDEPEND ?= "virtual/kernel:do_packagedata"
    do_rootfs[depends] += " \
        makedevs-native:do_populate_sysroot virtual/fakeroot-native:do_populate_sysroot ${LDCONFIGDEPEND} \
        virtual/update-alternatives-native:do_populate_sysroot update-rc.d-native:do_populate_sysroot \
        ${KERNELDEPMODDEPEND} \"

    KERNEL_DEPLOY_DEPEND ?= "virtual/kernel:do_deploy"
    do_build[depends] += "${KERNEL_DEPLOY_DEPEND}"

These sections might be relevant, but I'm not sure it's what I'm looking for. If anyone can give me some advice, very grateful.

I tried searching virtual/kernel.

openbmc\meta-openembedded\meta-oe\recipes-core\packagegroups\packagegroup-boot.bb is the one that most closely matches what I think I'm thinking of, but it seems that the core-image.bbclass uses the packagegroup-core-boot not packagegroup-boot.bb