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Sam Van den Eynde
Asked: 2020-02-01 07:04:33 +0800 CST

How can I build the kernel without compiling everything if I did that previously?

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I rebuild the kernel based on the git sources. These are the steps that I take:

  1. git clone git://kernel.ubuntu.com/ubuntu/ubuntu-focal.git
  2. cd ubuntu-focal
  3. vi debian.master/changelog
  4. apply patches
  5. fakeroot debian/rules clean binary-headers binary-generic

If I then apply another patch and want to compile the same version again, I get an error because certain folders are not empty. I can issue 'fakeroot debian/rules clean' to solve that, but then I need to compile the whole kernel.

Is there a way to recompiling only the changed files and build the debs based on that? It seems a trivial thing I just haven't figured out yet.

compiling kernel

1 Answers

  1. So it is not exactly what I was looking for, but as I am mainly looking to save some time and can spare the diskspace I adopted ccache based on this guide.

    I use the method described here to compile the kernel, with the exception that I pull in the sources from GregKH's stable tree.

    I added this to .bashrc:

    export CCACHE_DIR="/scrap/ccache"
export CC="ccache gcc"
export CXX="ccache g++"
export PATH="/usr/lib/ccache:$PATH"

    But it seems I have to add the parameter when invoking the build:

    CC="ccache gcc" fakeroot debian/rules binary-headers binary-generic

    Results after 2 identical builds look good (starting with empty cache then doing a build with everything in cache equals 50% hit rate in total):

    cache hit (direct) 20354
    cache hit (preprocessed) 81
    cache miss 20411
    cache hit rate 50.03 %
    called for link 94
    called for preprocessing 148
    unsupported code directive 12
    no input file 1329
    cleanups performed 0
    files in cache 61169
    cache size 7.3 GB
    max cache size 16.0 GB

    Regular Kernel builds took slightly over an hour. The first ccache run (filling the cache) took 95 minutes. The second build 30 minutes. I'm keeping it like this for now.

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