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README.pod

orbuild - a build system for OpenRISC

Instructions for the impatient

For the impatient user:

About orbuild

orbuild is a script framework that automatically downloads, builds, installs and tests a number of software components related to the OpenRISC processor architecture.

All the build steps are performed in parallel and there is an HTML report at the end with the overall build results, where you can click through to view each component build log separately.

Note that orbuild's framework is sufficiently generic so that it can be easily repurposed to build other projects.

Motivation

The OpenRISC project has grown and is now made up of many different components that need to be separately downloaded, configured and built. To many people, all these manual steps are a hassle, they just want to use the processor in their FPGA designs and have no interest in the supporting tools and technologies. orbuild is designed to automate the initial setup steps.

orbuild can also help OpenRISC developers to keep up. Changes in one component may negatively affect some other one and it's impractical to manually run all regression tests in all possible scenarios.

orbuild is not meant to be mandatory, it is just a helping hand which only performs standard downloads and software builds. Users and developers are or course free to ignore it and manuall perform the installation and test steps.

In the OpenRISC development community there is also the need to run a daily build with many possible component configurations, in order to alert the developers early when something has broken. This is in fact the main reason why orbuild was developed, and the first task it was actually used for.

The daily build can also take on the job of generating software releases, as manual release procedures often result in human error.

Objectives

  • Automatically download, configure, build, test and install the most common OpenRISC components locally.

    All users end up with the same directory structure.

  • Generate a daily build.

    Output directories are rotated by date, an HTML report is generated at the end. There is a top-level report and one individual report per task performed.

    Components are automatically packaged for off-line installation.

Audience

  • Users who wish to install many OpenRISC components at once
  • Developers who wish to test several OpenRISC components together
  • Daily build managers

Prerequisites

orbuild runs on Unix-like systems as well as in the Cygwin environment on Microsoft Windows. However, the most thoroughly tested platform is Linux.

Reasonably up-to-date versions of the following software are required: perl, bash, curl, subversion, git, GNU Make (tested with version 3.81).

Perl module XML::Parser is also required by the HTML report generator perl script.

Ubuntu/Debian Linux

Under Ubuntu/Debian systems, the following command installs all prerequisites (for the basic orbuild framework only) at once:

  sudo apt-get install autoconf build-essential make patch subversion git-core curl libxml-parser-perl gxmessage xdg-utils libnotify-bin

Each orbuild project has its own prerequisites. For the OpenRISC project, look at file Scripts/Projects/OpenRISC/README.pod .

Cygwin

Please make sure that your Cygwin is up to date. If you step through Cygwin's installation program without making any changes, all installed components will be upgraded to their latest versions.

Unfortunately, there does not seem to be a standard way to automatically install all the Cygwin packages listed below at once from the command line, so you'll have to do it manually. There is a third-party project called apt-cyg that may be worth investigating though.

Some of the required package names are:

  subversion
  make
  util-linux
  patch

Each orbuild project has its own prerequisites. For the OpenRISC project, look at file Scripts/Projects/OpenRISC/README.pod .

About orbuild versioning

orbuild follows a rolling release model: there are no official releases, you just get the current head status from the git repository.

Every now and then the main orbuild script version number gets updated, in order to provide some lose reference point.

Usage scenarios

How to get and build the OpenRISC components for the first time

The steps are (this example is for the bash shell):

   mkdir orbuild-2010-11-30
   cd    orbuild-2010-11-30

   git clone git://github.com/rdiez/orbuild.git

   # Edit the orbuild.config file, there should be little to change.
   # Take a look at file Scripts/Projects/OpenRISC/README.pod too for more information.

   # The very first time around, you may want to run the build in interactive mode
   # (with the --interactive switch), which disables parallel compilation but
   # allows you to enter your login and password for remote Subversion repositories
   # and so on. Afterwards, your credentials should get cached, and you should
   # not need the interactive mode any more.
   
   ./orbuild
   ./orbuild --resume    # (optional) resume a failed build, but see below for caveats

At the end, the user will probably find it convenient to set an environment variable like this, so that all other software will automatically find the just-built OpenRISC components:

   export OPENRISC_TOOLS="$PWD/Builds/<new subdir name>"

Run the following command for quick help text:

  ./orbuild --help      # Alternative:  perl orbuild --help

How to update and rebuild the OpenRISC components

There are several alternatives:

  • Create a new orbuild sandbox, optionally reusing downloaded files

    The safest way is to repeat the first-time scenario in a different directory.

    If the user wants to conserve Internet bandwidth, it should be safe to edit orbuild.conf in the new sandbox in order to share a global cache of downloaded tarball files.

  • Reuse the orbuild sandbox

    In order to further conserve Internet bandwidth, it is possible to reuse the orbuild sandbox and avoid checking out new copies of all repositories. The steps are:

       cd orbuild-2010-11-30
    
       # Update orbuild itself. This is optional but should be done often.
       # Otherwise, orbuild itself may not be up-to-date enough in order to build
       # the latest versions of all components.
       git pull
    
       ./orbuild --restart
       ./orbuild --resume    # (optional) resume a failed build, but see below for caveats
    
       # Switch to the new versions:     
       export OPENRISC_TOOLS="$PWD/builds/<new subdir name>"

Setting up a daily build server

The server administrator will probbly have to edit the orbuild.conf file and the project Makefile extensively in order to generate non-standard builds.

In addition to generating HTML report files, the server will probably want to send a notification e-mail to some mailing list at the end of the build. See file orbuild.conf for details.

How to resume a failed build

The build is designed to be a one-shot process: components are built just once, from beginning to end. However, if the build fails, it is possible to try and fix the problem in the local computer and resume from the last point of failure by issuing an ./orbuild --resume command. Resuming a build can save some time but is not always reliable. Therefore, when the resumed build completes successfully, you should re-build from scratch in order to make sure that those successful results are repeatable.

Why resuming is not reliable

When resuming, orbuild only moves forwards: components that were successfully built the last time around will never be rebuilt. There is no dependency checking at source-code level, and the installed tool versions are not checked either. Therefore, it is not safe to change any local build tools or update orbuild itself before resuming a build, as not all components will then be built with the same tool versions. Coping with such dependencies is well beyond the scope of this project.

The reasons why the results are not right may be subtle. Say component A builds successfully but component B fails because some library is not installed in your Operating System. If you install the library and resume the build, only component B will be built. However, if component A had seen the library installed the first time around, it may have enabled more features. Rebuilding from scratch may yield different results the next time around.

Resuming a build may fail even after interrupting it 'gently' with Ctrl+C, as most makefiles do not use the .DELETE_ON_ERROR: directive and the C compiler can then leave corrupted or zero-length object files behind. The next time around, those files will not be recompiled, and the linking phase will fail.

Note that the --resume switch will not update the source code repositories. If you want to build the most up-to-date components, you need to start the build from scratch.

Resuming a build while developing orbuid itself

If you are developing the orbuild makefiles themselves, keep in mind that a change in those makefiles will not trigger a rebuild of any affected components.

For example, adding a compiler flag to an application's makefile will not rebuild the related application.

Manually rebuilding a single component

After changing a component or an orbuild makefile, the safest way to test the changes is to rebuild all components from scratch. However, this can be time consuming, so rebuilding a single component may be desirable.

Depending on the orbuild project makefile and the specific component, it may be possible to rebuild just one component by deleting its output directory and/or the sentinel file it creates. Sentinel files are easy to find, all their names end in ".OrbuildSentinel". In order to rebuild a single component every time, which can be handy during development, you could temporarily add a line like this near the top of the makefile:

  $(shell rm $(ORBUILD_COMMAND_SENTINELS_DIR)/ORPSOCv2_LINT_OR1200.Cmd.$(ORBUILD_SENTINEL_FILENAME_SUFFIX))

Rebuilding a component will trigger a rebuild of anything else that depends on it, but only if the build succeeds. If a component fails to build, dependent components will not be rebuilt, but may still be flagged as successfully built in the final report, as the individual report files from previously successful builds will still be around on disk.

orbuild cannot automatically delete outdated reports files, as it does not keep track of each single component itself, but relies instead on GNU Make to handle components and its dependencies. That's also the reason why, when the build fails, orbuild will report all succeeded and failed components, but not those that were not even tried because some of their dependencies had already failed to build.

Directory structure

This is what the directory structure looks like:

  orbuild-2010-11-30/

    Scripts/             # orbuild's own source code

    DownloadCache/       # All tarballs downloaded from the Internet.

    Repositories/        # All git and subversion repositories downloaded from the Internet.

    Builds/
      build-2011-02-19/  # The build from yesterday.
        gnu-src-obj/
        gnu-src-bin/
        ...
        build-report/

      build-2011-02-20/  # Files being built now.
        ...

    orbuild            # The main script.
    orbuild.conf
    orbuild.status     # Contains the current destination subdir name "build-2011-02-20-23:59"
    orbuild.version    # The orbuild sandbox layout version. After a "git pull",
                       # the new layout may no longer be compatible with the existing one.
    README.pod         # This file.

The orbuild.conf configuration file

Why a configuration file is needed

Unfortunately, the user often needs to edit the configuration file, if only for the first time. For example, the Subversion repositories on the opencores.org web site require a login and password and they need to be entered interactively, so it may necessary to run the build at least once in interactive mode (but see command-line switch --interactive).

Most users will probably want to set up the visual notification feature, in order to start using the build as soon as it is finished.

OpenRISC developers may want to specify which repository branch should be checked out. (not implemeted yet)

Daily build administrators may want to temporarily build a specific component version if the latest one is known to be broken.

A graphical user interface able to edit the config file would be a nice addition to this project.

Configuration file format

orbuild.conf is a text file in simplified .INI file format. There are no [sections], all entries have the form "key = value", and lines starting with # are considered comments.

Please see the configuration file (which is well commented) for more information.

Caveats

About interactive builds and Subversion credentials

Normally, a build process should be completely automated, but often some sort of human interaction is needed, especially the very first time. For example, most Subversion repositories on the http://opencores.org/ web site require a login and password, which are manually entered once and then cached for any subsequent runs. In its default configuration, orbuild will run the build in such a way that anything requiring use interaction (like prompting for a password) will fail.

At first, I considered adding login and password configuration entries to orbuild.conf, so that they can be passed to Subversion on the command line, but then it would be too easy to forget this fact and publish a build log which makes your password visible in clear text.

In order to run a build in interactive mode, pass the --interactive command-line switch to orbuild (see related settings ParallelBuild and InteractiveBuild in file orbuild.conf). Running the build in interactive mode disables parallel compilation, which will slow down the process significantly. Therefore, once all the passwords are cached, you will probably want to run the build in non-interactive mode the next time around.

Parallel builds can overload the computer

A parallel build process can easily overload the system, cause thrashing and render the computer unresponsive for long periods of time. orbuild's efforts to prevent that from happening are rudimentary at best. If you are serious about constraining your system load, you'll have to resort to more powerful methods like cgroups under Linux, or running the build inside a virtual PC.

How to write sub-makefiles with regards to parallel builds

Configuration setting Makefile = xxx in file orbuild.conf specifies the top-level makefile that will be driving the build. In order to avoid overloading the computer (which would cause thrashing), orbuild sets a global limit on the number of build sub-processes that should run in parallel, see the GNU Make documentation for the -j switch for more information.

When the top-level makefile starts further instances (child processes) of GNU Make, it passes along information about how to talk back to the top-level GNU Make instance in order to coordinate the build. This information is located in environment variable MAKEFLAGS and looks like this:

  <...other flags...>  --jobserver-fds=3,4 -j

This way, GNU Make makes sure that the parallel limit is not exceeded across the whole build process. Note that this limit is not enforced in any hard way, as child processes are actually free to start as many sub-processes as they like. Overstepping the parallel limit is not usually fatal, it just increases the risk of overloading the computer.

For GNU Make's limit mechanism to work, all sub-makefiles and child build scripts must obey the following rules:

  • All parallel process creation must be performed with GNU Make. Other build tools will probably not respect the global limit.
  • No-one else can specify his own "-j x" value, as that disables the global coordination mechanism.

    Only orbuild is allowed to set the -j limit for the top-level makefile. If you don't clear MAKEFLAGS manually, you will be able to easily identify other places that do, as they generate this warning:

      warning: -jN forced in submake: disabling jobserver mode.
  • The "--jobserver-fds=x,y -j" information must be passed along in the MAKEFLAGS environment variable.

    orbuild can help you extract that information where it is normally needed, see the xxx_MAKEFLAGS_FILTER variables in the bundled example makefiles.

    Note that, if you do not call the sub-makefile directly from the parent makefile, but indirectly over some other script, GNU Make may not automatically pass the necessary information, and you'll get this warning further down the line:

      warning: jobserver unavailable: using -j1. Add `+' to parent make rule.

    Just add a '+' character at the beginning of your rule. For example, this rule:

      target.o:
        script_that_runs_make.sh

    becomes then:

      target.o:
        +script_that_runs_make.sh

    Consult the GNU Make documentation for details.

Unfortunately, most third-party build scripts tend to specify their own -j x value, so the global limit will not be honoured at that point. Some of them allow the user to disable the parallel build, but then they tend to pass -j 1 along, which is also not ideal, as parallel building is always disabled for the related build step, even when the parent makefile and the current parallel limit would allow it.

orbuild does follow the above rules: if the parallel build is disabled in the configuration file, it will not pass any -j flag to GNU Make. That makes the build process sequential while still allowing for parallel building if orbuild itself has been started from a higher-level makefile in parallel build mode.

Beware that some makefiles do not support parallel execution. In those cases, the calling makefile/script should filter the "--jobserver-fds=x,y -j" information out of MAKEFLAGS (the easiest way is to clear MAKEFLAGS completely). Without that information, the makefile will run sequentially. Explicitly specifying "-j 1" has no further effect but does not harm either.

Repository skew

At the beginning of the daily build, all source code repositories are updated in order to downloada the latest file versions. The update itself is not atomic: if a developer checks in changes to one of the repositories during the update process, it's not clear whether the new or the old file versions will be picked up by today's build.

In order to minimize the risk of such skew across the repositories, the daily build could take the current date/time as today's baseline and check out all repositories at that timestamp. However, the following issues remain unresolved:

  • There may be a realtime clock skew across the different repository servers.
  • Git may deliver the wrong results for a given timestamp.

    If a developer merges a branch into head, and then tries to check out head as of last week, git may go down the merged branch and return a different set of files as it would have been the case had the deloper done a check out last week.

    In order to prevent that from happening, git developers must follow this kind of rules:

    • Never do a non-fast-forward (i.e., forced) push.
    • Never have any clock skew.
    • Always merge features into master (not the other way around).

      Upstream should always merge with --no-ff, which usually means making upstream an automated process, and not a human being using "git push".

      Or maybe never do "git merge", but "git rebase" instead. Rebasing ensures that the commits are always re-applied so that the history stays linear.

    • Always push immediately after committing on master.

    Under those conditions, it would be possible to retrieve consistent results with "git log -1 --first-parent --until=...".

Year 2038 compliance

Some of the perl scripts use mktime and the like and are not year 2038 compliant on 32-bit Linux systems and on Cygwin.

Why orbuild is written in perl, bash and make

There are a number of open-source build frameworks (see section "Alternatives to orbuild" below) that could take on the task of building software components. However, at the time orbuild was developed, they seemed overkill. Besides, most OpenRISC users would not be prepared to install and configure such complex software systems in order to get the build running on their machines. Perl, Bash and Make are very popular and should be easy to install on all systems, if they are not already there.

The original author of orbuild was already familiar with Perl and had no experience with Python, Ruby and so on. The dash shell would be faster, but speed is not so important here, and bash has more features.

Makefiles are hard to write, linear scripts would have been much easier to maintain. However, GNU Make has a killer feature: all make subprocesses coordinate with each other in order to limit the amount of concurrent processes and keep the system's load within the given limit, see section "How to write sub-makefiles" for more information. Note that the user can always set the number of concurrent processes to 1 (sequential processing), in order to keep his PC responsive for other tasks.

The orbuild tools are written so that they can be easily reused or adapted for other projects. In fact, most of them have evolved over the years in other unrelated projects.

GitSvnMirror

This project contains a set of tools to create and maintain a collection of read-only Git mirrors of Subversion repositories, see subdirectory Scripts/GitSvnMirror for more information.

Alternatives to orbuild

  • Use a fully-fledged continuous integration server like Apache Continuum, CruiseControl, BuildBot or Hudson/Jenkins.
  • Create a top-level Git or Subversion repository where each component is a git submodule or a Subversion external reference.

    This is only a partial solution, as it would allow the user to easily fecht or update all source code repositories, but without any further build steps.

Feedback

Please send feedback to rdiezmail-openrisc at yahoo.de

The project's official web site is https://github.com/rdiez/orbuild

License

Copyright (C) R. Diez 2011, rdiezmail-openrisc at yahoo.de

The orbuild source code is released under the GPL 3 license.

Please note that some of the files distributed with orbuild have other authors and licenses.

This document is released under the Creative Commons Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0) license.

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