tor-browser-build/README.HACKING

Hacking on Tor Browser Build
============================

This file tries to list the main things to know when making changes to
the Tor Browser build.


rbm documentation
-----------------

If you go to directory rbm/doc, you can find the rbm documentation. You
can build it with 'make html' or 'make man'.


Using and defining options
--------------------------

Options can be used in templates with the following syntax:

  [% c("option_name") %]

More details about the templates syntax can be found in
rbm/doc/rbm_templates.7 and [http://template-toolkit.org/docs/manual/index.html].

Some options have a specific meaning to rbm. You can see their descriptions
in rbm/doc/rbm_config.7 and rbm/doc/rbm_input_files.7.

When the option does not have a specific meaning to rbm, it is a good
idea to define it under var/ to avoid potential conflicts in option names
with a future version of rbm.

The options can be defined in different places:

- rbm.conf for options available to all components
- project/$project/config for options available to one component
- rbm.local.conf for user defined options

In each of those places, an option can be defined:

- at the root of the document
- under targets/$target/, in which case the definition only applies when
  a specific target is defined

The targets are usually used to select:

- the platform: torbrowser-linux-x86_64, torbrowser-linux-i686,
  torbrowser-windows-i686, torbrowser-osx-x86_64
- the channel: release, nightly, alpha

The targets torbrowser-linux-x86_64, torbrowser-linux-i686,
torbrowser-windows-i686, torbrowser-osx-x86_64 are special cases. They
do not contain options directly, instead they contain a list of other
targets. For instance, the torbrowser-linux-x86_64 target is pointing
to the linux-x86_64 and linux targets. You should define an option under
the linux target if it applies to Linux on both architectures, or under
the linux-x86_64 if it only applies to the x86_64 architecture.

An option that is defined at the root of rbm.conf can be overridden by
an other definition under a target, or inside projects/$project/config.
You can find the complete priority order in rbm/doc/rbm_config.7.


Defining a project's filename
-----------------------------

The filename option defines the output file or directory from the build
of a component. If the file or directory exists in the out/$component
directory, the component will not be rebuilt when it is used as a
dependency from an other component.

The filename is usually something like this:

  filename: '[% project %]-[% c("version") %]-[% c("var/osname") %]-[% c("var/build_id") %].tar.gz'

The var/build_id value is a hash that is based on the build inputs of
the component:
 - the build script (after template evaluation)
 - the container definition
 - the input files (the filename when it is a dependency on an other
   project, the filename and hash of its content otherwise)
This means that each time the build script, the container or one of the
dependencies is modified, the output filename will change and a rebuild
of the component will be required.

The version and var/osname values could be removed from the filename,
but they are useful to get an idea of what a file contains.


Adding some Linux/Windows/OSX specific changes to a build script
----------------------------------------------------------------

You can use the following template syntax in the build scripts:

  [% IF c("var/linux") -%]
    # do something for linux
  [% ELSIF c("var/windows") -%]
    # do something for windows
  [% ELSIF c("var/osx") -%]
    # do something for osx
  [% END -%]

You can also use var/linux-x86_64 and var/linux-i686 for things that
only apply to x86_64 and i686 linux builds. You can use the var/release,
var/alpha and var/nightly options to do things depending on the channel.

As an alternative you can define an option with a different value
depending on the target:

  targets:
    linux:
      var:
        do_something: 'do something for linux'
    windows-i686:
      var:
        do_something: 'do something for windows'
    osx-x86_64:
      var:
        do_something: 'do something for osx'

And in the build script, use:

  [% c("var/do_something") %]


Evaluating a component's build script
-------------------------------------

If you want to look at the build script used to build a component for a
specific platform/channel, you can use the following command:

   $ ./rbm/rbm showconf $component build --target $channel --target $platform

$component should be replaced by the name of the component.

$channel should be one of the following:

 - release

 - alpha

 - nightly

$platform should be one of the following:

 - torbrowser-linux-x86_64

 - torbrowser-linux-i686

 - torbrowser-windows-i686

 - torbrowser-osx-x86_64

For example, to see tor's build script for linux x86_64 on the alpha
channel, you can use:

  $ ./rbm/rbm showconf tor build --target alpha --target \
    torbrowser-linux-x86_64

If the component you are looking at has many dependencies, the display
can take some time as various build_id values need to be computed. If
you don't care about the accuracy of input and output file names, you
can add '--target no_build_id' to the command line. For instance, if you
want to look at the build script for the tor-browser component (which
has a lot of dependencies), you can use:

  $ ./rbm/rbm showconf tor build --target alpha --target \
     torbrowser-linux-x86_64 --target no_build_id

The same type of commands can be used to look at any option values,
replacing build with the name of the option you want to look at. For
instance, if you want to know the output filename of tor on linux-x86_64
on the alpha channel, you can use:

  $ ./rbm/rbm showconf tor filename --target alpha --target \
    torbrowser-linux-x86_64


Building a single component
---------------------------

When you are working on some changes to a component, before creating a
full bundle with those changes, you might want to try a build of the
component you modified only.

This can be done with the following command:

   $ ./rbm/rbm build $component --target $channel --target $platform

See the previous section "Evaluating a component's build script" for a
list of possible values for $channel and $platform.

For instance, if you want to build tor for linux-x86_64 on the alpha
channel, you can run:

   $ ./rbm/rbm build tor --target alpha --target torbrowser-linux-x86_64

To find the resulting file from the build, you can use 'ls -ltr out/tor/'
to find the file with the last modification time.


Patching Firefox (or an other component)
----------------------------------------

If you want to test a Firefox patch, the easiest way to do it is to
copy the patch file to the projects/firefox/ directory, then edit
projects/firefox/config to add the new patch to the list of input_files:

  - filename: patch-for-XXXX.patch

Then edit projects/firefox/build to add a line somewhere (probably just
before running the configure script) to apply the patch:

  patch -p1 < $rootdir/patch-for-XXXX.patch

You can now run 'make testbuild' (or an other build target) to start a
build with the patch.

As an alternative, if you have your patch in a git repository, you can
edit projects/firefox/config to change the git_url option to point to
your git repository, and change the git_hash option to point to the
commit you want to build. If the new git_hash option is not pointing to
a signed tag, you will also need to comment the 'tag_gpg_id: 1' line.
The git_hash option can point to a tag, a commit, a branch or anything
that is understood by git.

If you specify a branch in the git_hash option, you don't need to prefix
it with a git remote name as all branches from the git repository
selected in the git_url option are created as local branches.

If you want to work on a local git repository, it is not a good idea to
work on the git_clones/firefox repository directly. Instead you should
create a separate git repository and update the git_url option with a
file:// URL pointing to your repository.

After changing the git_url option or when new commits have been added
to a branch, you should run "make fetch" before starting a build to get
the new commits. If you want to fetch new commits automatically when
starting a new build you can add a "fetch: 1" line to
projects/firefox/config.

Remember that the git_hash option has different definitions for alpha
and nightly builds, so you should modify the right one depending on
what type of build you are doing (see also the "Types of builds" section).


The Firefox mozconfig files
---------------------------

In the gitian build, we are using the mozconfig files included in the
tor-browser.git repository (the .mozconfig, .mozconfig-mac and
.mozconfig-mingw files).

In the rbm build however, we need to make some small modifications to
those files, so we are instead using mozconfig files stored in the
projects/firefox/ directory, ignoring the .mozconfig files from the
tor-browser.git repository.

This could change in the future, when we are not using Gitian anymore.


Debugging a build error
-----------------------

If the build fails, a debugging shell will automatically be opened in
the container used for the build (unless you set debug to 0 in
rbm.local.conf).

Before using the debugging shell, you can first look at the build logs
in an other terminal (the filename of the log file is indicated in the
rbm output).

In the debug shell, you can type 'bash' to get a shell with completion.
You can then look at the 'build' file, and copy paste some of its commands
to debug the problem. If you need to edit files, vim is not installed
in the build containers, but vi can be used instead.

When you press ctrl+d (twice if you opened a bash shell) the debug shell
is closed and the container containing the failed build is removed.

The path to the container should be printed on the screen in case you
want to backup its rootfs to be able to look at it later.


Testing an rbm patch
--------------------

When you are working on a patch to rbm, you might want to try a Tor
Browser build using your patched version of rbm. You could patch the
rbm in the rbm/ directory, however your patch can be reverted if you
use any of the makefile rules that does a 'git submodule update'.
To avoid this you can clone the rbm git repository to a separate
directory, where you will apply your patch. To do a build using your
patched rbm, take the command from the makefile, but replace $(rbm)
with the path to your patched rbm.

For example, if you want to try a Linux x86_64 alpha build, you can run:
  $ /path_to_rbm/rbm build release --target alpha --target \
                                                torbrowser-linux-x86_64


Types of builds: nightly, alpha, release and testbuild
------------------------------------------------------

The testbuild makefile target allows you to do a build quickly in the
testbuild directory, skipping the generation of all the locales and the
mar files. This is useful during development.

By default the testbuild is based on the alpha build. All the options
can have a different definition for the alpha, release and nightly builds.
Usually the git_hash option has a different definition for the nightly
builds in order to point to the master branch.

If you want your testbuild target to create builds based on nightly
rather than alpha, you can edit your rbm.local.conf file and uncomment
the targets/torbrowser-testbuild definition.