Development Guidelines

Development Environment

Required Toolchain

The easiest way to get a working toolchain is to run make crossgcc in the toplevel directory of a coreboot checkout. Distributions usually modify their compilers in ways incompatible with coreboot. If in doubt, use our toolchain.

The toolchain consists of:

• GNU development environment:
  • GCC with G++
  • binutils
• libncurses*-dev
• IASL, now part of the ACPICA download (package pmtools or iasl in many distributions)

Coding Guidelines

General Guidelines

• Encapsulate and isolate assembly language
• Code shall not be "commented out"
• No use of floating-point arithmetics
• No hiding of identifiers defined in outer scopes
• Typedefs are unique (device_t?)
• Functions shall have prototype declarations
• Local functions should be declared static
• No function definitions in header files
• All variables are assigned before use
• All objects should have fully qualified types (unsigned int instead of unsigned)
• Types which indicate signedness and bitness should be used (uint32_t or u32 instead of unsigned int)
• We suggest trying to import more such rules, such as additional ones described in MISRA-C 2012 (Guidelines for the use of C in critical systems)

Variable types

Whenever possible, please use a variable type which is explicit about the size of data it can hold. For example, use uint32_t or u32 instead of unsigned long when referencing a 32-bit wide register.

short int names vs stdint names

There is currently no hard rule on whether one should use short int types (u32), or stdint types (uint32_t). Whichever type you elect to use, please use common sense and stay consistent.

Assembly Language

To keep the code consistent across the different supported platforms, AT&T syntax is to be used through-out the project. We are working actively on replacing the existing Intel syntax code with AT&T syntax. No new Intel syntax code is allowed into the project.

It is highly encouraged to not use inline assembly, but instead to encapsulate and isolate the use of assembly language to pure assembly files.

Comments

References

If you are referencing a data sheet or other documentation in the code, please add the name or document number in addition to the URL. Vendors just love to rearrange their websites (and some remove documentation on their old products altogether)! If we have the name/number (or even just the filename of the PDF) at least there's a chance to google for it again (either on the vendor's site or on some archive).

Coding Style

• We use the coreboot Coding Style throughout the project.
• You can use the 'indent' tool to fix the coding style like this:

indent -npro -kr -i8 -ts8 -sob -l80 -ss -ncs *.[ch]

Do not trust 'indent' blindly, though. It sometimes gets things wrong. Manual corrections may be required.

The 80 character limit

Lines larger than 80 columns should be broken down into readable pieces. This includes not only source files, but also Makefiles, Kconfig files, and any file meant to be edited by a human. We recommend setting your editor to show the 80th character limit. This limit is not a relic from long forgotten times, but a very practical and efficient way to organize code and increase productivity. Several files can be edited on the same monitor, without the need to side-scroll. Side-scrolling source files is inefficient, time-consuming, and uncomfortable. On average, 95% of source lines are shorter than 80 characters, so limiting the line length is this manner is not only _not_ an impediment, it also gets you to think on how to best organize the code.

Documentation Guidelines

General Guidelines and Tips

• Documentation should be put into the wiki and/or in the code as Doxygen comments
• Avoid using different styles and looks of documentation
• Document why and what, not how (No comments like /* add one to i */)
• Document assumptions, stipulations etc...
• Document design and concepts!
• Not lots of documentation but good documentation
• Structured documentation
• Focus: Whom are you addressing in your documentation? Write documentation for users, developers, vendors, ...

Automatic documentation

• Doxygen-generated API- and code documentation is available at http://qa.coreboot.org/docs/. This documentation is updated on every 10th checkin.
• To create a Doxygen comment, write

/**
 * Sample comment.
 */

or

/** Sample comment. */

• There are a few commands that describe what kind of comment you are adding:

@param — input parameters of a function

@return — return value of a function

• A list of all commands is available at http://www.stack.nl/~dimitri/doxygen/commands.html

Full example:

/**
 * Calculate the length of a string.
 *
 * @param str The input string.
 * @return The length of the string, not including the final NUL character.
 */
static inline size_t strlen(const char *str)
{
        /* ... */
}

Testing

Every commit will be processed by the autobuild and autotest system available at http://qa.coreboot.org/. In addition please run autobuild yourself before submitting patches.

autobuild

Autobuild can be found at coreboot/util/abuild.

Please run abuild before you commit.

Autobuild is also running on every check-in to the repository. The results of this build are also available at http://qa.coreboot.org/.

autotest

We can also run automatic tests on boards, if we find contributors willing to have a board automatically managed by our QA system. This requires a permanent connection to the net, a host system and some special circuitry. If interested, please contact us using the mailing list.

How to contribute

Creating Patches

• We use gerrit for change management, using the instance on http://review.coreboot.org/
• While not necessary with gerrit, make sure that your change is against current master. Patches that fail on merge (after some developer looked at it and approved it) might linger around until you update it.
• Rebase, if necessary, then test again. You might be the only contributor with that specific mainboard.
• Make sure all new and modified files contain the proper license headers (see below).
• Make sure all added files are actually within the commit.
• Make one commit per logical change.
• For more details on using gerrit, see our Git documentation. Things are somewhat different (eg. it's normal to rebase changes that were already pushed).
• Double-check that your changes are correct, and that the commit only contains what you think it contains.

Sign-off Procedure

We employ a similar sign-off procedure for coreboot as the Linux kernel developers do. Please add a note such as

Signed-off-by: Random J Developer <random@developer.example.org>

to your email/patch if you agree with the following Developer's Certificate of Origin 1.1.

Patches without a Signed-off-by cannot be pushed to gerrit!

You have to use your real name in the Signed-off-by line and in any copyright notices you add. Patches without an associated real name cannot be committed!

Developer's Certificate of Origin 1.1:

By making a contribution to this project, I certify that:

(a) The contribution was created in whole or in part by me and I have
the right to submit it under the open source license indicated in the file; or

(b) The contribution is based upon previous work that, to the best of my
knowledge, is covered under an appropriate open source license and I have the
right under that license to submit that work with modifications, whether created
in whole or in part by me, under the same open source license (unless I am
permitted to submit under a different license), as indicated in the file; or

(c) The contribution was provided directly to me by some other person who
certified (a), (b) or (c) and I have not modified it; and

(d) In the case of each of (a), (b), or (c), I understand and agree that
this project and the contribution are public and that a record of the contribution
(including all personal information I submit with it, including my sign-off) is
maintained indefinitely and may be redistributed consistent with this project or the
open source license indicated in the file.

Note: The Developer's Certificate of Origin 1.1 is licensed under the terms of the Creative Commons Attribution-ShareAlike 2.5 License.

Reviews

• Send your patch to gerrit for review.
  • Provide useful commit messages. Explain what the change does and why. Our short intro to git explains the format in more detail.
  • Add a single line containing your "sign-off" after the description of the patch (git commit -s helps, but make sure you understand and comply with the DCO).
    • Example: Signed-off-by: John Doe <john@example.com>
• The developers will review and/or test your change and send comments or suggestions. Please push updated patches as described in "evolving patches".
• If the change looks ok to one or more developers, they will approve and submit it to the master branch.

Bug-Tracker

Issues can be documented at https://ticket.coreboot.org/.

License Issues

• Contributed code must be GPL'd (preferrably 'GPLv2', but 'GPLv2 or any later version' is fine, too). At the very minimum the code must have a GPLv2-compatible license.

Common License Header

Please quote the shortened GPL license header text in every file, as shown below. It should contain:

• The year(s) when the code was written or modified and a copyright note of you (or your company, if you are contributing as part of your employment, and thus the copyright belongs to your company). Also, please provide an email address if possible so that you can be contacted if questions arise.
  • Example:

Copyright (C) 2006 John Doe <john@example.com>

Copyright (C) 2004-2006 Company, Inc.

• The full GPL header as shown below.

Complete example for *.c and *.h files:

/*
 * This file is part of the coreboot project.
 *
 * Copyright (C) 2003-2005 Jane Doe <jane@example.com>
 * Copyright (C) 2006 Company, Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2 of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

Complete example for Makefiles, config files, Python files, shell scripts etc.:

##
## This file is part of the coreboot project.
##
## Copyright (C) 2003-2005 Jane Doe <jane@example.com>
## Copyright (C) 2006 Company, Inc.
##
## This program is free software; you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation; version 2 of the License.
##
## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
##