GCC GIT mirror

There is a read-only git mirror of the gcc svn repository available at:

http://gcc.gnu.org/git/gcc.git
git://gcc.gnu.org/git/gcc.git
git+ssh://gcc.gnu.org/git/gcc.git

It can be browsed at repo.or.cz.

Getting started - Read-Only

To work with get a local clone of the public repository is required. This is close to a svn checkout, however copies the complete history. Therefore commands like "git log", "git status", "git diff", "git blame" can be executed very fast and without internet connect.

Create the clone (git <= 1.6.4 warning)

> git clone git://gcc.gnu.org/git/gcc.git

Now the repository is available in "gcc". Try some commands

> cd gcc
~/gcc> git status
# On branch trunk
nothing to commit (working directory clean)

To fetch changes from the official svn-mirror repository into trunk

~/gcc> git pull --rebase

To extract patches for submission, use

~/gcc> git format-patch origin/trunk

On branches

Our repository already contains a set of important gcc branches

List the available branches

~/gcc> git branch -a
* trunk
  remotes/origin/HEAD -> origin/trunk
  remotes/origin/fortran-dev
  remotes/origin/gc-improv
  remotes/origin/gcc-4_0-branch
  remotes/origin/gcc-4_1-branch
  remotes/origin/gcc-4_2-branch
  remotes/origin/gcc-4_3-branch
  remotes/origin/gcc-4_4-branch
  remotes/origin/gccgo
  remotes/origin/graphite
  remotes/origin/ifunc
  remotes/origin/ix86
  remotes/origin/lw-ipo
  remotes/origin/master
  remotes/origin/melt-branch
  remotes/origin/microblaze
  remotes/origin/profile-stdlib
  remotes/origin/reload-v2a
  remotes/origin/split
  remotes/origin/spu-4_5-branch
  remotes/origin/transactional-memory
  remotes/origin/trunk

To work with one of these branches we need a local branch we can edit.

~/gcc> git checkout -b gccgo origin/gccgo
Checking out files: 100% (2204/2204), done.
Branch gccgo set up to track remote branch gccgo from origin.

Updates are the same as for trunk

~/gcc> git pull --rebase

Advanced Usage

The above works fine for browsing the repository and simple hacking, but has various issues. Here's what seems to me to be the optimal way of using git-svn with the GCC repository. Please email (jason) or grosser@ if you have any questions/issues with these instructions.

Commit upstream (git-svn)

The simple repository we create above is only read only. To commit changes upstream patches have to be extracted and committed using svn. However there is a way to commit changes directly out of git: git-svn

Commit on trunk

We start based with the read only repository create above.

Add git-svn support to be able to commit

# Use this exact SVN url for gcc.git and git-svn to work together.
# Adding an SSH username to the url is ok.
# git svn init -s svn+ssh://username@gcc.gnu.org/svn/gcc
~/gcc> git svn init -Ttrunk --prefix=origin/ svn+ssh://gcc.gnu.org/svn/gcc

# Update index and fetch changes
~/gcc> git svn fetch

# Ignore the same files that SVN does.
~/gcc> git svn show-ignore >> .git/info/exclude

Integrate the latest upstream changes in the local repository

~/gcc> git pull --rebase

See the list of changes we are going to commit

~/gcc> git diff origin/trunk..trunk

Commit our local changes into the official gcc subversion repository

~/gcc> git svn dcommit

Commit on branches

A single branch

To commit on a branch available in origin/* just add it git-svn

~/gcc> git config --add svn-remote.svn.fetch branches/gccgo:refs/remotes/origin/gccgo
~/gcc> git svn fetch

"git svn dcommit" commits automatically to the svn branch that the local branch you are working on was created from. So if you start with

~/gcc> git checkout -b gccgo origin/gccgo

and keep committing on top of this, the dcommit will commit onto the gccgo branch in svn.

All branches

~/gcc> git config --add remote.origin.fetch refs/remotes/*:refs/remotes/origin/*
~/gcc> git config --add svn-remote.svn.fetch branches/*:refs/remotes/origin/*
~/gcc> git svn fetch

Pulling all branches increases the size of the .git directory by about 30% over just trunk and release branches.

The various release branches

# GCC
~/gcc> for f in 2_95 3_0 3_1 3_2 3_3 3_4 ; do git config --add remote.origin.fetch refs/remotes/gcc-$f-branch:refs/remotes/origin/gcc-$f-branch; done
~/gcc> for f in 2_95 3_0 3_1 3_2 3_3 3_4 ; do git config --add svn-remote.svn.fetch branches/gcc-$f-branch:refs/remotes/origin/gcc-$f-branch; done

# egcs
~/gcc> for f in 1_00 1_1; do git config --add remote.origin.fetch refs/remotes/egcs_${f}_branch:refs/remotes/origin/egcs_${f}_branch; done
~/gcc> for f in 1_00 1_1; do git config --add svn-remote.svn.fetch branches/egcs_${f}_branch:refs/remotes/origin/egcs_${f}_branch; done

~/gcc> git svn fetch

Subdirectory branches

If you want a branch that lives in a subdirectory of branches, such as redhat/gcc-4_4-branch, you can't get it from the gcc.git mirror for some reason, so leave out the remote.origin.fetch line for that branch (and don't use the wildcard fetch commented out above), and use git svn fetch to fetch the branch from SVN:

~/gcc> git config --add svn-remote.svn.fetch branches/redhat/gcc-4_4-branch:refs/remotes/origin/redhat/gcc-4_4-branch
~/gcc> git svn fetch

Usage

Pull changes from the git mirror as desired using

git pull

or from the SVN repository (e.g. if you need a change that isn't in the git mirror yet, or are working on a branch that isn't in the git mirror) using

git svn rebase

I routinely do both of these to update my tree, depending on the circumstance: * git pull without --rebase gives a nice summary of what files have been updated, and will pull into a dirty working tree, and preserves the timestamps on files that aren't affected by the pull, but does a merge if I have any local commits; * git svn rebase grabs any very recent changes and rebases my local commits on top of the current SVN head in preparation for a checkin.

You probably don't want to use git svn fetch other than for the initial import of a branch, as shown above.

To look at your local changes, use

git log -p trunk..

To push all of them to the SVN server, use

git svn dcommit

Working with other branches

To switch your current working directory to a different branch, first set up a local tracking branch:

git checkout -b gcc44 gcc-4_4-branch

Then you can switch between branches with

git checkout master
git checkout gcc44

To make a separate working directory for hacking on another branch at the same time, you can just create a new checkout. Referencing the old repository ~/gcc saves a lot of space and bandwidth.

# Make sure the main repository is up to date; see below
> (cd ~/gcc; git remote update)
> git clone --references=~/gcc git://gcc.gnu.org/git/gcc.git branch
> cd branch
~/branch> git checkout -b mywork origin/branch

Adding git-svn or more branches or doing pull/rebase/dcommit works as with your main repository. This repository should be significantly smaller than the main one as it only contains the changes on the branch itself. It uses your main repository for anything on the trunk. In fact, if you do this for a branch that's already in your main repository, the .git directory in the new repository will be less than 10MB. If you pull in this repository sooner than in the main one, you'll get a few duplicate objects here, but you can clean them up with 'git gc'. You can use this repository without doing anything in your trunk repository as long as you don't delete the trunk repository or remove branches that this one is using.

The first "git remote update" is to work around an apparent shortcoming of the "alternates" functionality (at least with 1.6.4): if the alternate repository doesn't have the objects at the heads of *all* the branches you are fetching with the initial fetch, git's quickfetch fails and it will download everything. So if your main repository is even one commit behind the head of any branch, git will re-download the whole shebang all over again. So we need to make sure that the main repository is fully up to date before we do the initial fetch.

Note that using git cherry-pick to copy changes between SVN branches brings along svn metadata which could confuse git-svn into thinking you're on a different SVN branch, so be sure to do a git commit --amend to edit the commit message before dcommitting to the new branch.

Make your changes available online

To allow others to view your changes online or to pull your changes in their repositories you can make (parts) of your git repository available on services like repo.or.cz or gitorious.org.

Already available gcc forks at repo.or.cz

Let's start with creating a fork of the gcc git mirror. Go to the "Fork" page, select "push" mode and add project name, password, email and captcha. For this example the fork is called "fancyfork".

Now you have to signup as user here with login, email, and ssh public key. If you "edit" your new repository you can add the new user as committer.

Add our online repository to the local one

~/gcc> git remote add repo-or-cz ssh://repo.or.cz/srv/git/official-gcc/fancyfork.git

To make the local branch "mylocalbranch" available, push the branch to repo-or-cz

~/gcc> git push repo-or-cz mylocalbranch

New changes to already published branches can be pushed by just using

~/gcc> git push repo-or-cz

Others can now watch your activities online, add your fork as another remote repository to their local repository or just clone your fork.

Usage hints for git

git-merge-changelog

Before long you'll get frustrated with git's handling of ChangeLog merges, which is just as bad as SVN's. But there's a fix for that!

git clone git://git.savannah.gnu.org/gnulib.git
cd gnulib
./gnulib-tool --create-testdir --dir=/tmp/testdir123 git-merge-changelog
cd /tmp/testdir123
./configure
make
make install
git config --global merge.merge-changelog.name "GNU-style ChangeLog merge driver"
git config --global merge.merge-changelog.driver "/usr/local/bin/git-merge-changelog %O %A %B"
echo "ChangeLog   merge=merge-changelog" >> ~/gcc-git/.git/info/attributes

NOTE: git-merge-changelog used to be extremely slow for cherry-picking changes from trunk to release branches, but this was fixed with a change on 2009-07-02.

Update bash function

Here's my generic "update this source tree" bash function. When I want to rebase, I do that manually either with 'git svn rebase' or 'git rebase -i trunk'

up() { if [ -d CVS ]; then cvs -q update "$@";
       elif [ -d .svn ]; then svn up "$@";
       elif gitd=`git rev-parse --git-dir 2>/dev/null`; then
           if [ -f $gitd/objects/info/alternates ]; then
               for d in `cat $gitd/objects/info/alternates`; do
                   (cd $d; git fetch)
               done
           fi
           if [ -d $gitd/patches ] && `stg top 2>/dev/null`; then
               stg pull
           else
               git pull
           fi
       fi; }

rebase -i

git rebase -i is a very useful tool for organizing local changes for svn dcommit.

If I want to update a patch other than the current one, I just check in my current work and use git rebase -i to move it up the list and squash it into my earlier patch. Another approach would be to stash my current changes, tell rebase -i to edit the patch I want to change, pop the stash and then commit --amend.

If I want to apply some but not all of my current commits to SVN, I use git rebase -i to move the ones I want to apply to the top of the list, select "edit" for the last one I want to apply, and do git svn dcommit before git rebase --continue.

Useful aliases

Here are some aliases I'm finding useful (to add to your ~/.gitconfig). Note that these only work with the advanced setup due to differences in the branch.$BRANCH.merge config.

[alias]
        st = status
        ci = commit
        br = branch
        co = checkout
        sr = svn rebase
        sci = svn dcommit
        # The current branch.
        cbr = "!expr `git symbolic-ref HEAD` : 'refs/heads/\\(.*\\)'"
        # The branch being tracked by the current branch.
        track = "!git config --get branch.`git cbr`.merge"
        # Show all the local commits on this branch.
        lg = "!git log -p `git track`.."
        # Write all the local commits to ~/patch, filtering out modifications to ChangeLog files
        lgp = "!git log -p `git track`.. | filterdiff -x '*/ChangeLog' | sed -e '/^diff.*ChangeLog/{N;d}' > ~/patch"
        # Show all the local changes on this branch as one big diff.
        df = "!git diff `git track`"
        dfc = diff --cached
        # Reorganize the local commits on this branch.
        rb = "!git rebase -i `git track`"
        rc = rebase --continue
        # 'git rmerge mybranch' to reintegrate a temporary branch onto the top of the current branch
        rmerge = "!f(){ cur=`git cbr`; git rebase $cur $1; git rebase $1 $cur; }; f"

Old Information

Below here is information that no longer describes my use of git, but that other people might find interesting.

Stacked Git

I used to find Stacked Git useful for hacking on GCC, since it makes it easy to pop off patches that I'm still working on so I can check the one I've just finished testing into SVN. But lately I've stopped using it and just use git branches directly.

With stg, if I want to remove a commit from my tree temporarily and come back to it later, I do

stg uncommit mypatchname [myotherpatchname...]
stg pop -a

and then when I want to work on it again,

stg push mypatchname [myotherpatchname...]
stg commit

This way stg only knows about unapplied patches, so it won't get confused when I do a 'git pull'.

And I periodically look at the list of suspended patches with

stg series

Making Patches

I currently make patches for gcc-patches using my 'git lgp' alias, below.

However, git always produces unified diffs, while the GCC project policy is to prefer context diffs. I don't bother with this, but if you really want to make a context diff, you can create a wrapper script somewhere:

cat > ~/bin/git_diff_wrapper <<EOF
#! /bin/sh
exec diff -p -L "$1" "$2" "$5" | cat
EOF
chmod +x ~/bin/git_diff_wrapper

and when you want to make a context diff for submitting a patch, do

GIT_EXTERNAL_DIFF=git_diff_wrapper git diff trunk

Further Reading

An introduction to git-svn for Subversion/SVK users and deserters

git-svn workflow