From where in Android source code do they download the kernel?

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http://stackoverflow.com – I am trying to delve myself into the android source code, and I realized that Android source code do not contain pre-compiled kernels for many devices (such as Samsung toro, etc). So, I presume that Android download necessary kernels as they are built, but I can't find the code where they actually perform kernel downloads. I found few relevant files such as "generate-factory-images-package.sh" or "generate-packages.sh", but they do not seem to perform actual downloading process. Can someone point me toward the code where Android actually fetch necessary kernels? Thank you! (HowTos)