Hi I recently noticed that alternating between "make" and "make targz-pkg" rebuilds the whole Kernel. This was not happening before. As a Kernel developer, my build/install/test environment heavily relies on the fact that "make targz-pkg" only quickly generates the tarball if everything is already built, so this change is heavily impacting my development environment. I did some bisection and concluded that the first bad commit is: commit 9c8fa9bc08f60ac657751daba9fccf828a36cfed Author: Masahiro Yamada Date: Sat May 7 15:48:26 2016 +0900 kbuild: fix if_change and friends to consider argument order I also verified that if I just revert this commit on top of the most recent tree it goes back to the usual behavior. I read the commit message and it seems that some unneeded rebuilds are somewhat expected, but I can't understand why such a change in the command line like the one I did triggers everything to be rebuilt. IMHO, it really shouldn't. I also wonder that maybe the regression I'm experiencing was not expected in the original change, so maybe there's a way to keep the original improvement caused by the mentioned patch without the regression I'm experiencing. How to reproduce (exact commands I used at every bisect step): $ make tinyconfig $ time make -j4 V=2 # this should build things $ time make -j4 V=2 # just to make sure nothing will be rebuilt $ time make -j4 V=2 targz-pkg In bad commits, the last command will trigger a rebuild of the whole Kernel, mentioning "due to command line change" as a reason to rebuild every object file. In good commits, the last command will finish after a few seconds, not rebuilding anything, just giving us a nice tarball. Also notice that if you do wait for the whole targz-pkg build, and later go back to "make -j4 V=2" (without targz-pkg), it will, again, rebuild everything, which is also not the old behavior. After some investigation, it looks like the .obj.cmd files are what's compared here, so let me provide you an example that will hopefully help you debug: $ time make -j4 V=2 $ cp init/.main.o.cmd /tmp/main-before.cmd $ time make -j4 V=2 targz-pkg $ diff -Nrup /tmp/main-before.cmd init/.main.o.cmd > /tmp/cmd- diff.patch You can access the diff file here: https://people.freedesktop.org/~pzanoni/cmd-diff.patch If you take a look, you'll see that the only difference is that the cmd file generated during targz-pkg contains these extra chars in the cmd_init/main.o declaration: -nostdinc -isystem /usr/lib/gcc/x86_64-linux-gnu/5/include But please notice that these arguments are repeated! The main- before.cmd file contains those arguments only once, while the new file contains them twice. I don't know why "make targz-pkg" makes these arguments appear twice. Maybe fixing this would be a better way to solve the regression instead of just reverting the "first bad commit"? I didn't debug the problem further. I'm hoping the info I provided is enough for you to keep things moving, but if you have any patches or tips on where I could continue digging, please tell me. I suppose the problem should be easily reproducible everywhere. In the meantime, since I can't pay the price of 2 full rebuilds for every tested Kernel, I suppose I'll be carrying a local revert, but I'd be really happy to see an upstream solution. Thanks, Paulo��.n��������+%������w��{.n�����{��F���{ay� ʇڙ���f���h������_�(�階�ݢj"��������G����?���&��
