CONTRIBUTING.md

   1 Authors: Jason Lowe-Power
   2          Andreas Sandberg
   3          Steve Reinhardt
   4
   5 If you've made changes to gem5 that might benefit others, we strongly encourage
   6 you to contribute those changes to the public gem5 repository. There are
   7 several reasons to do this:
   8  * Share your work with others, so that they can benefit from new functionality.
   9  * Support the scientific principle by enabling others to evaluate your
  10    suggestions without having to guess what you did.
  11  * Once your changes are part of the main repo, you no longer have to merge
  12    them back in every time you update your local repo. This can be a huge time
  13    saving!
  14  * Once your code is in the main repo, other people have to make their changes
  15    work with your code, and not the other way around.
  16  * Others may build on your contributions to make them even better, or extend
  17    them in ways you did not have time to do.
  18  * You will have the satisfaction of contributing back to the community.
  19
  20 The main method for contributing code to gem5 is via our code review website:
  21 https://gem5-review.googlesource.com/. This documents describes the details of
  22 how to create code changes, upload your changes, have your changes
  23 reviewed, and finally push your changes to gem5. More information can be found
  24 from the following sources:
  25  * http://gem5.org/Submitting_Contributions
  26  * https://gerrit-review.googlesource.com/Documentation/index.html
  27  * https://git-scm.com/book
  28
  29
  30 High-level flow for submitting changes
  31 ======================================
  32
  33     +-------------+
  34     | Make change |
  35     +------+------+
  36            |
  37            |
  38            v
  39     +------+------+
  40     | Post review |
  41     +------+------+
  42            |
  43            v
  44     +--------+---------+
  45     | Wait for reviews | <--------+
  46     +--------+---------+          |
  47            |                      |
  48            |                      |
  49            v                      |
  50       +----+----+   No     +------+------+
  51       |Reviewers+--------->+ Update code |
  52       |happy?   |          +------+------+
  53       +----+----+                 ^
  54            |                      |
  55            | Yes                  |
  56            v                      |
  57       +----+-----+   No           |
  58       |Maintainer+----------------+
  59       |happy?    |
  60       +----+-----+
  61            |
  62            | Yes
  63            v
  64     +------+------+
  65     | Submit code |
  66     +-------------+
  67
  68 After creating your change to gem5, you can post a review on our Gerrit
  69 code-review site: https://gem5-review.googlesource.com. Before being able to
  70 submit your code to the mainline of gem5, the code is reviewed by others in the
  71 community. Additionally, the maintainer for that part of the code must sign off
  72 on it.
  73
  74 Cloning the gem5 repo to contribute
  75 ===================================
  76
  77 If you plan on contributing, it is strongly encouraged for you to clone the
  78 repository directly from our gerrit instance at
  79 https://gem5.googlesource.com/.
  80
  81 To clone the master gem5 repository:
  82  > git clone https://gem5.googlesource.com/public/gem5
  83
  84 Other gem5 repositories
  85 -----------------------
  86
  87 There are a few repositories other than the main gem5 development repository.
  88
  89  * public/m5threads: The code for a pthreads implementation that works with
  90    gem5's syscall emulation mode.
  91
  92 Other gem5 branches
  93 -------------------
  94
  95 None right now.
  96
  97 Making changes to gem5
  98 ======================
  99
 100 It is strongly encouraged to use git branches when making changes to gem5.
 101 Additionally, keeping changes small and concise and only have a single logical
 102 change per commit.
 103
 104 Unlike our previous flow with Mercurial and patch queues, when using git, you
 105 will be committing changes to your local branch. By using separate branches in
 106 git, you will be able to pull in and merge changes from mainline and simply
 107 keep up with upstream changes.
 108
 109 Requirements for change descriptions
 110 ------------------------------------
 111 To help reviewers and future contributors more easily understand and track
 112 changes, we require all change descriptions be strictly formatted.
 113
 114 A canonical commit message consists of three parts:
 115  * A short summary line describing the change. This line starts with one or
 116    more keywords (found in the MAINTAINERS file) separated by commas followed
 117    by a colon and a description of the change. This line should be no more than
 118    65 characters long since version control systems usually add a prefix that
 119    causes line-wrapping for longer lines.
 120  * (Optional, but highly recommended) A detailed description. This describes
 121    what you have done and why. If the change isn't obvious, you might want to
 122    motivate why it is needed. Lines need to be wrapped to 75 characters or
 123    less.
 124  * Tags describing patch metadata. You are highly recommended to use
 125    tags to acknowledge reviewers for their work. Gerrit will automatically add
 126    most tags.
 127
 128 Tags are an optional mechanism to store additional metadata about a patch and
 129 acknowledge people who reported a bug or reviewed that patch. Tags are
 130 generally appended to the end of the commit message in the order they happen.
 131 We currently use the following tags:
 132  * Signed-off-by: Added by the author and the submitter (if different).
 133    This tag is a statement saying that you believe the patch to be correct and
 134    have the right to submit the patch according to the license in the affected
 135    files. Similarly, if you commit someone else's patch, this tells the rest
 136    of the world that you have have the right to forward it to the main
 137    repository. If you need to make any changes at all to submit the change,
 138    these should be described within hard brackets just before your
 139    Signed-off-by tag. By adding this line, the contributor certifies the
 140    contribution is made under the terms of the Developer Certificate of Origin
 141    (DCO) [https://developercertificate.org/].
 142  * Reviewed-by: Used to acknowledge patch reviewers. It's generally considered
 143    good form to add these. Added automatically.
 144  * Reported-by: Used to acknowledge someone for finding and reporting a bug.
 145  * Reviewed-on: Link to the review request corresponding to this patch. Added
 146    automatically.
 147  * Change-Id: Used by Gerrit to track changes across rebases. Added
 148    automatically with a commit hook by git.
 149  * Tested-by: Used to acknowledge people who tested a patch. Sometimes added
 150    automatically by review systems that integrate with CI systems.
 151
 152 Other than the "Signed-off-by", "Reported-by", and "Tested-by" tags, you
 153 generally don't need to add these manually as they are added automatically by
 154 Gerrit.
 155
 156 It is encouraged for the author of the patch and the submitter to add a
 157 Signed-off-by tag to the commit message. By adding this line, the contributor
 158 certifies the contribution is made under the terms of the Developer Certificate
 159 of Origin (DCO) [https://developercertificate.org/].
 160
 161 It is imperative that you use your real name and your real email address in
 162 both tags and in the author field of the changeset.
 163
 164 For significant changes, authors are encouraged to add copyright information
 165 and their names at the beginning of the file. The main purpose of the author
 166 names on the file is to track who is most knowledgeable about the file (e.g.,
 167 who has contributed a significant amount of code to the file).
 168
 169 Note: If you do not follow these guidelines, the gerrit review site will
 170 automatically reject your patch.
 171 If this happens, update your changeset descriptions to match the required style
 172 and resubmit. The following is a useful git command to update the most recent
 173 commit (HEAD).
 174
 175  > git commit --amend
 176
 177 Posting a review
 178 ================
 179
 180 If you have not signed up for an account on the Gerrit review site
 181 (https://gem5-review.googlesource.com), you first have to create an account.
 182
 183 Setting up an account
 184 ---------------------
 185  1. Go to https://gem5.googlesource.com/
 186  2. Click "Sign In" in the upper right corner. Note: You will need a Google
 187  account to contribute.
 188  3. After signing in, click "Generate Password" and follow the instructions.
 189
 190 Submitting a change
 191 -------------------
 192
 193 In gerrit, to submit a review request, you can simply push your git commits to
 194 a special named branch. For more information on git push see
 195 https://git-scm.com/docs/git-push.
 196
 197 There are three ways to push your changes to gerrit.
 198
 199 Push change to gerrit review
 200 ----------------------------
 201
 202  > git push origin HEAD:refs/for/master
 203
 204 Assuming origin is https://gem5.googlesource.com/public/gem5 and you want to
 205 push the changeset at HEAD, this will create a new review request on top of the
 206 master branch. More generally,
 207
 208  > git push <gem5 gerrit instance> <changeset>:refs/for/<branch>
 209
 210 See https://gerrit-review.googlesource.com/Documentation/user-upload.html for
 211 more information.
 212
 213 Pushing your first change
 214 --------------------------
 215 The first time you push a change you may get the following error:
 216
 217  > remote: ERROR: [fb1366b] missing Change-Id in commit message footer
 218  > ...
 219
 220 Within the error message, there is a command line you should run. For every new
 221 clone of the git repo, you need to run the following command to automatically
 222 insert the change id in the the commit (all on one line).
 223
 224  > curl -Lo `git rev-parse --git-dir`/hooks/commit-msg
 225    https://gerrit-review.googlesource.com/tools/hooks/commit-msg ; chmod +x
 226    `git rev-parse --git-dir`/hooks/commit-msg
 227
 228 If you receive the above error, simply run this command and then amend your
 229 changeset.
 230
 231  > git commit --amend
 232
 233 Push change to gerrit as a draft
 234 --------------------------------
 235
 236  > git push origin HEAD:refs/drafts/master
 237
 238 Push change bypassing gerrit
 239 -----------------------------
 240
 241 Only maintainers can bypass gerrit review. This should very rarely be used.
 242
 243  > git push origin HEAD:refs/heads/master
 244
 245 Other gerrit push options
 246 -------------------------
 247
 248 There are a number of options you can specify when uploading your changes to
 249 gerrit (e.g., reviewers, labels). The gerrit documentation has more
 250 information.
 251 https://gerrit-review.googlesource.com/Documentation/user-upload.html
 252
 253
 254 Reviewing patches
 255 =================
 256
 257 Reviewing patches is done on our gerrit instance at
 258 https://gem5-review.googlesource.com/.
 259
 260 After logging in with your Google account, you will be able to comment, review,
 261 and push your own patches as well as review others' patches. All gem5 users are
 262 encouraged to review patches. The only requirement to review patches is to be
 263 polite and respectful of others.
 264
 265 There are multiple labels in Gerrit that can be applied to each review detailed
 266 below.
 267  * Code-review: This is used by any gem5 user to review patches. When reviewing
 268    a patch you can give it a score of -2 to +2 with the following semantics.
 269    * -2: This blocks the patch. You believe that this patch should never be
 270      committed. This label should be very rarely used.
 271    * -1: You would prefer this is not merged as is
 272    * 0: No score
 273    * +1: This patch seems good, but you aren't 100% confident that it should be
 274      pushed.
 275    * +2: This is a good patch and should be pushed as is.
 276  * Maintainer: Currently only PMC members are maintainers. At least one
 277    maintainer must review your patch and give it a +1 before it can be merged.
 278  * Verified: This is automatically generated from the continuous integrated
 279    (CI) tests. Each patch must receive at least a +1 from the CI tests before
 280    the patch can be merged. The patch will receive a +1 if gem5 builds and
 281    runs, and it will receive a +2 if the stats match.
 282  * Style-Check: This is automatically generated and tests the patch against the
 283    gem5 code style (http://www.gem5.org/Coding_Style). The patch must receive a
 284    +1 from the style checker to be pushed.
 285
 286 Note: Whenever the patch creator updates the patch all reviewers must re-review
 287 the patch. There is no longer a "Fix it, then Ship It" option.
 288
 289 Once you have received reviews for your patch, you will likely need to make
 290 changes. To do this, you should update the original git changeset. Then, you
 291 can simply push the changeset again to the same Gerrit branch to update the
 292 review request.
 293
 294  > git push origin HEAD:refs/for/master
 295
 296 Note: If you have posted a patch and don't receive any reviews, you may need to
 297 prod the reviewers. You can do this by adding a reply to your changeset review
 298 on gerrit. It is expected that at least the maintainer will supply a review for
 299 your patch.
 300
 301 Committing changes
 302 ==================
 303
 304 Each patch must meet the following criteria to be merged:
 305  * At least one review with +2
 306  * At least one maintainer with +1
 307  * At least +1 from the CI tests (gem5 must build and run)
 308  * At least +1 from the style checker
 309
 310 Once a patch meets the above criteria, the submitter of the patch will be able
 311 to merge the patch by pressing the "Submit" button on Gerrit. When the patch is
 312 submitted, it is merged into the public gem5 branch.