WOW! That is fantastic! Thanks for sharing. - Will
> On Mar 22, 2016, at 1:36 PM, Ryan Lovelett <swift-...@ryan.lovelett.me> wrote: > > On Tue, Mar 22, 2016, at 01:26 PM, William Dillon wrote: >> >>> >>> Phew. Well I finally got everything ready to where I could bisect >>> binutils. I won't bore with the details of what it took to actually be >>> able to bisect binutils (unless someone actually wants to know). >> >> I would be interested if it’s not too much trouble. I’ve been in a similar >> predicament with LLVM before. I’d love to have another tool in the chest in >> case I have to do such a thing again. >> >> - Will > > Not too much trouble at all. In fact, I kind of just want to tell > someone; so I'm glad you asked! > > The biggest challenge of the whole thing was just getting reproducable > builds using binutils. For the better part of a week I was unable to > build a linker that could link even the most basic "Hello World" source. > Eventually I ended up contacting the binutils package maintainer, Allan > McRae. > > He pointed out that in order to build binutils on Arch there was a > specific order of operations. You have to build the > linux-api-headers->glibc->binutils->gcc->binutils->glibc. This was > especially true because of the change in the way that relocations occurs > in the newer binutils. Since Arch is "rolling release" distribution I > ended up having to make a VM that had a configuration of Arch from early > February, when I knew all this stuff worked. Once I could compile newer > versions of binutils and that made all the difference. > > Now that I had a stable process for building binutils the next parts > were relatively straight forward. When I set out to do this I had > _thought_ what I am about to describe would be all I'd need to do. > > Effectively I went back to a version/commit of binutils that I new > worked. I new the last version that worked was package 2.25.1-3; so I > got the commit hash from the PKGBUILD script [1] that was used to make > that package. Which turned out to be 2bd25930. Next I wanted the commit > hash of the package that I knew didn't work 2.26-3; so I got the commit > hash from PKGBUILD script [2] that was used to make that package. Which > turned out to be 71090e7a. > > Generally speaking that would have been enough to actually do the > bisecting. However since I knew the compilation loops were going to be > long I realized this could take a few hours of compiling and rinse and > repeat to actually find the script. Luckily `git bisect run` exists. > > `git bisect run` is effectively like manual `git bisect` except you can > write a script that performs the action you'd perform at each step of > the bisect. > > From there I wrote a script that provided the steps to build binutils > from source. Then install that new binutils and compile Swift with that > updated version. The actual script that I used is right here [3]. > > The script ensures that the system gets back to a "pristine" state > between bisection steps and then compiles and installs binutils. It then > compiles Swift. > > If anything goes wrong compiling binutils then its considered a > skippable commit and the script returns 125. If Swift fails to compile > it was considered a "bad" commit and the script returns 1. If Swift > compiled cleanly it was a "good" commit and the script returns 0. > > The most important advice I can give you is don't forget the 125 return > code. If something goes wrong and you prematurely mark a commit as "bad" > then the entire bisect can complete but erroneously tell you which > commit was actually the first bad commit. In my opinion its better to > skip than prematurely mark as bad. > > Once the script was written the hard part was over. > > $ cd /directory/with/binutils/source > $ git bisect start 71090e7a9dde8d28ff5c4b44d6d83e270d1088e4 > 2bd25930221dea4bf33c13a89c111514491440e2 > $ git bisect run ~/binutils-bisect.sh |& tee -a ~/bisect-output.log > > I put all of the logs and scripts in a Gist just in-case I ever need > them again in the future [4]. > > Hope that was enough information Will. > > [1] > https://projects.archlinux.org/svntogit/packages.git/diff/trunk/?h=packages%2Fbinutils&id=d5de6c456d1391bf802b675b1b6227f5dd3b7073&context=40&ignorews=0&dt=0 > [2] > https://projects.archlinux.org/svntogit/packages.git/commit/trunk?h=packages/binutils&id=97e6d52b49ff3882a3ec7a5833ceb4569ac5d914 > [3] > https://gist.github.com/RLovelett/f73fb5f701035b33417c#file-binutils-bisect-sh > [4] https://gist.github.com/RLovelett/f73fb5f701035b33417c _______________________________________________ swift-dev mailing list swift-dev@swift.org https://lists.swift.org/mailman/listinfo/swift-dev
