Re: git bisect with history manipulation

From: Sean <seanlkml@sympatico.ca>
Date: Oct 23, 2006, 15:47 UTC
Message-ID: <BAYC1-PASMTP01856E85F8D54BE3CBF69EAE000@CEZ.ICE>
In-Reply-To: <a425f86c0610230722r2a0ae473o467d303f915b6c1e@mail.gmail.com>

On Mon, 23 Oct 2006 17:22:41 +0300 "Kalle Pokki" <kalle.pokki@iki.fi> wrote:

Show 22 quoted lines

> I'm still pretty new with git, and cannot quite figure out how to use
> "git bisect" effectively in this special case: I'm running an embedded
> powerpc board, to which I need about a dozen platform patches in the
> kernel. Originally I made the patches with quilt on top of 2.6.15.4. I
> recently started using git, and just applied the patches on top of
> v2.6.18. However, the system seems to oops at every boot now. So I did
> "git branch downgrade && git reset --hard v2.6.15" and applied my
> patches on top of it to create a starting state similar to what I had
> previously. There everything is ok.
> 
> Wanting to try to bisect the kernel versions, I then merged the master
> branch into the downgrade branch. Then I marked my last platform
> commit as good, and v2.6.18 as bad. However the bisect algorithm seems
> to group the platform patches near v2.6.18 instead of v2.6.15, since I
> don't have the platform files in the bisect checkout. And since I
> don't have the platform files, I can't compile a kernel that would run
> on my board.
> 
> So is there any way to insert a few patches to an arbitrary point
> backwards in time and start bisecting from that to the present time?
> Or am I thinking this somehow all wrong?
>

Well, there is no way to insert the patches into the history at an old point so that they're always available at each bisection point in your search. The history is immutable.

What you will have to do, is apply your patches manually at each bisection point before you compile/test. After testing you'll have to remove your manual patches and continue with your next git bisect command. However, there are a few ways that you can make this easier to do.

You could use the Stacked Git utility (which is a Quilt like clone built on top of Git) to help you along in this process. Actually, you may be able to do the same thing with Quilt itself, but i don't know i've never used it.

That said, i'll try to outline one way to do this that should work using just native Git commands. The first thing you need to do is prepare a git branch based on the first known-good commit that contains all your extra patches. So:

$ git checkout -b mypatches v2.6.15 $ patch < patch1 $ git commit -a $ patch < patch2 $ git commit -a etc...

Then you can go back to the master branch and start the bisection:

$ git checkout master $ git bisect start $ git bisect bad $ git bisect good v2.6.15

At which point git will create and move you to a temporary "bisect" branch to do your compile/testing. Now before you compile, you want to append your patch series from the branch you prepared earlier, so:

$ git pull . mypatches

Now compile and test. After you've tested, you will have to remove your patches from this branch before continuing with the git bisection process so:

$ git reset --hard ORIG_HEAD

And now continue with your bisection, let's assume the first bisection point still didn't work:

$ git bisect bad

Which will move you to a new bisection point where you can go back to the "git pull . mypatches" step to apply your patch series again and do another compile/test. Continue with this process as needed.

Hope that is clear enough, Sean